- stunnel-users - stunnel.org

Re: Stunnel Show Log Window
by Jose Alf. 31 May '26

31 May '26

Hi Graham, Yes. You are absolutely right. I was a bit confused with your question at first. I apologize. If we don't uncomment the output=filename.ext line, the log lines won't be written to any disk file. In this case, On Windows, the log lines go to the Log Window you mention. This is implemented as a circular buffer kept in RAM with hardcoded capacity for 1000 lines. That is, you will only see the last 1000 lines sent to the log and older lines are silently discarded. No crashes should happen. Best Regards,Jose -- On Sunday, May 31, 2026 at 10:57:37 AM GMT-5, Graham Jones <graham(a)lorien56.co.uk> wrote: Hi Jose, Thanks for the explanation about stunnel.log My config file has the line: ;output = stunnel.log I understand this to mean that the file stunnel.log is NOT created. And there is no evidence of this file anywhere. But the GUI allows me to see a "log window". So my question is: what happens when this "log window" fills up? Regards, == Graham > -----Original Message----- > From: Josealf.rm [mailto:[email protected]] > Sent: 31 May 2026 12:46 > To: Graham(a)lorien56.co.uk > Subject: Re: [stunnel-users] Stunnel Show Log Window > > Hi Graham, > > Stunnel does not implement automatic log rotation and it will not overwrite > earlier log entries. It will always try to append new entries at the end. By > default, the log file is named stunnel.log. If you run out of storage, stunnel > will probably crash. In Unix-like OSes like Linux or FreeBSD, you can configure > OS tasks to gracefully handle the log management. Periodically the stunnel > server process is stopped, the oldest log file is deleted and/or compressed > and the newest/current log is renamed. Then stunnel is started and a new > stunnel log is created. In Windows you could do something similar by creating > a suitable script or batch file and running it via Task Scheduler. > > Regards > Jose > > > > On 31/05/2026, at 1:26 AM, Graham Jones via stunnel-users <stunnel- > users(a)lists.stunnel.org> wrote: > > > > I'm new to Stunnel. > > > > stunnel 5.78 on x64-pc-mingw32-gnu platform Windows 7 Pro. > > > > I see the option to "Show Log Window". I have read the manual. I see > there > > is an option to specify an output file; I am not using this option. > > > > My question: > > > > When the space allocated to the log information fills up, what happens? > > Does stunnel overwrite the oldest log entries first? Or does it crash? > > > > Regards, > > > > == Graham > > > > > > _______________________________________________ > > stunnel-users mailing list -- stunnel-users(a)lists.stunnel.org > > To unsubscribe send an email to stunnel-users-leave(a)lists.stunnel.org

2 2

Stunnel Show Log Window
by Graham Jones 31 May '26

31 May '26

I'm new to Stunnel. stunnel 5.78 on x64-pc-mingw32-gnu platform Windows 7 Pro. I see the option to "Show Log Window". I have read the manual. I see there is an option to specify an output file; I am not using this option. My question: When the space allocated to the log information fills up, what happens? Does stunnel overwrite the oldest log entries first? Or does it crash? Regards, == Graham

2 1

Certificate rejected ...?
by Graham Jones 31 May '26

31 May '26

I'm new to Stunnel. stunnel 5.78 on x64-pc-mingw32-gnu platform Windows 7 Pro. During installation, the process walked me through the creation of a certificate. I have these settings: [Lopham-imap] client = yes accept = 127.0.0.1:52143 connect = mail.lopham.co.uk:993 CAfile = ca-certs.pem The connection succeeds. I add the following lines: verifyChain = yes checkHost = mail.lopham.co.uk OCSPaia = yes The connection fails with the following lines in the log: 2026.05.30 21:45:52 LOG5[2]: Service [Lopham-imap] accepted connection from 127.0.0.1:51901 2026.05.30 21:45:52 LOG5[2]: s_connect: connected 193.143.227.10:993 2026.05.30 21:45:52 LOG5[2]: Service [Lopham-imap] connected remote server from 127.0.0.1:51902 2026.05.30 21:45:52 LOG4[2]: CERT: Pre-verification error: certificate not found in local repository: self-signed certificate in certificate chain 2026.05.30 21:45:52 LOG4[2]: Rejected by CERT at depth=1: OU=generated by AVG Antivirus for SSL/TLS scanning, O=AVG Web/Mail Shield, CN=AVG Web/Mail Shield Root 2026.05.30 21:45:52 LOG3[2]: SSL_connect: tls_post_process_server_certificate@ssl/statem/statem_clnt.c:2124: error:0A000086:SSL routines::certificate verify failed: client 127.0.0.1:51901 2026.05.30 21:45:52 LOG5[2]: Connection closed/reset: 0 byte(s) sent to TLS, 0 byte(s) sent to socket I see it finds the self-signed certificate in certificate chain. Why is this rejected? Any ideas, please? Regards, == Graham

3 3

stunnel works but only with debug on
by Graham Jones 28 May '26

28 May '26

I'm new to stunnel. stunnel 5.78 on x64-pc-mingw32-gnu platform Windows 7 Pro Using Outlook to open a connection to a POP server Extract from stunnel.conf [Zen-pop3] client = yes accept = 127.0.0.1:110 connect = mailhost.zen.co.uk:995 CAfile = ca-certs.pem With debug = 7 the test succeeds. The log shows: 2026.05.13 16:49:06 LOG5[4]: Service [Zen-pop3] accepted connection from 127.0.0.1:49596 2026.05.13 16:49:06 LOG5[4]: s_connect: connected 212.23.1.19:995 2026.05.13 16:49:06 LOG5[4]: Service [Zen-pop3] connected remote server from 127.0.0.1:49598 2026.05.13 16:49:06 LOG5[4]: Connection closed: 59 byte(s) sent to TLS, 202 byte(s) sent to socket With ;debug a test connection fails after about 20 seconds delay. Log extract: 2026.05.13 17:22:05 LOG5[6]: Service [Zen-pop3] accepted connection from 127.0.0.1:53162 2026.05.13 17:22:05 LOG5[6]: s_connect: connected 212.23.1.11:995 2026.05.13 17:22:05 LOG5[6]: Service [Zen-pop3] connected remote server from 127.0.0.1:53163 2026.05.13 17:22:26 LOG3[6]: SSL_connect: Connection reset by peer (WSAECONNRESET) (10054) Why does it only work with debug enabled? Any ideas, please? Regards, == Graham

2 1

[PATCH 0/3] LDAP server-side STARTTLS support
by Steffen Heil | secforge 13 May '26

13 May '26

Hi Michal, This series adds server-side STARTTLS support for the LDAP protocol handler (RFC 2830). Three patches are attached: 0001 — core feature (src/protocol.c only) 0002 — automated test plugin for make check 0003 — optional Docker-based live integration test [RFC] Background ---------- stunnel already supports LDAP STARTTLS on the client side (ldap_client_middle): it connects to an LDAP backend, sends a StartTLS ExtendedRequest, waits for the success response, and then performs the TLS handshake toward the backend. The server side was missing. Without it, stunnel could not act as a TLS termination proxy in front of a plain LDAP backend for clients that initiate connections using STARTTLS — a common deployment pattern where legacy LDAP clients that do not support LDAPS (TLS-on-connect) still expect to negotiate TLS via STARTTLS before sending credentials. Patch 1 — core feature ----------------------- Two new functions in src/protocol.c, mirroring the structure of the existing client-side implementation: ldap_server_init Sets connect_before_ssl=1 so stunnel establishes the TCP connection to the backend before starting the TLS handshake with the local client. ldap_server_middle Reads the incoming LDAPMessage from the client and validates it as a StartTLS ExtendedRequest (APPLICATION 23, OID 1.3.6.1.4.1.1466.20037). Extracts the messageID and sends back a well-formed StartTLS ExtendedResponse (APPLICATION 24, resultCode=success) with the matching messageID. stunnel then performs SSL_accept with the client. WinLDAP-style four-byte length encoding is handled, matching the existing client-side behaviour. Both functions are registered in the PROTOCOL dispatch table under the existing "ldap" name, so protocol = ldap now works for both client and server services. Patch 2 — automated tests -------------------------- p28_ldap_starttls.py adds two tests to make check: Test 281: the Python test harness performs the RFC 2830 StartTLS exchange directly against a stunnel server (protocol=ldap), then upgrades to TLS via asyncio's loop.start_tls(), exercising ldap_server_middle in isolation. Test 282: a full client→server proxy chain where both stunnel instances run with protocol=ldap, exercising ldap_client_middle and ldap_server_middle together end-to-end. Patch 3 — live integration test [RFC / optional] ------------------------------------------------- ldap_starttls_live_test.sh is a shell script that runs against a real OpenLDAP server (osixia/openldap) in Docker. It requires Docker, ldapsearch/ldapadd, and openssl, so it is not part of make check. I'm sending it as an optional follow-up in case it is useful for manual verification or as a starting point for a CI stage. Feel free to drop it if it does not fit the project's test infrastructure. License ------- I dedicate my contributions in this patch series to the public domain, in line with the contribution policy stated in CREDITS.md. Regards, Steffen Heil Geschäftsführer _______________________________________________________________________________ secforge GmbH Starterzentrum | Campus A1.1 | 66123 Saarbrücken | Deutschland Phone: +49 179 2339260 | +49 681 93355440 E-Mail: steffen.heil(a)secforge.de<mailto:[email protected]> Web: https://www.secforge.de Registergericht: Amtsgerichts Saarbrücken | HRB 109882 Geschäftsführer: Steffen Heil, Dr. Mikhail Kovalev

1 0

client UDP 5093 -> TCP 5555 and vice versa in Server (TCP 5555 -> UDP 5093)
by admin＠igram.gr 19 Apr '26

19 Apr '26

Hi, I have a project where several students with IBM SPSS installed need to connect to a server where the IBM SPSS Network License Manager (Sentinel RMS) is installed and it requires that UDP port 5093 be open on the server's firewall to allow the clients to communicate and retrieve licenses. In my case this is not allowed in the firewall and I am trying to find solutions. One solution is to create VPN users to ensure that only allowed clients can communicate on this port (UDP 5093). But I prefer to keep the port closed for everyone. So the question is of it is possible with stunnel to convert / wrap e.g. by users the UDP port 5093, to "convert" it to TCP e.g. 5555 thus bypassing the firewall policy on the server side (TCP/UDP 5093 is not allowed), and on the server side to do the reverse, i.e. the "conversion" from TCP 5555 to UDP 5093 or is it a stupid idea? Has anyone done a similar project? THX John

2 1

[PATCH] checkPurpose configuration to circumvent EKU
by stunnel＠benary.org 14 Apr '26

14 Apr '26

From: benaryorg <binary(a)benary.org> What this does in a nutshell is to allow to use client certificates for servers, and server certificates for clients. This has become a relevant workaround for people using Let's Encrypt certificates for mutual TLS authentication (i.e. checkHost on both sides). Let's Encrypt, due to pressure from Google, have disabled client usage in their certificates, thereby causing issues in the latest renewals. https://letsencrypt.org/2025/05/14/ending-tls-client-authentication Any connections initiated by a client using a server certificate as to authenticate against a server cause a "unsuitable certificate purpose" on the server side and a TLS termination on the client side. This patch allows to simply override this check, for better or for worse. An earlier version was written with `checkPurpose` being allowed to occur multiple times (like `checkHost` and friends). However the value set does not support binary OR (it is simply sequentially numbered). Signed-off-by: benaryorg <binary(a)benary.org> --- doc/stunnel.8.in | 7 +++++++ doc/stunnel.html.in | 8 ++++++++ doc/stunnel.pod.in | 8 ++++++++ src/options.c | 35 +++++++++++++++++++++++++++++++++++ src/prototypes.h | 1 + src/verify.c | 3 +++ 6 files changed, 62 insertions(+) diff --git a/doc/stunnel.8.in b/doc/stunnel.8.in index db02292..4450715 100644 --- a/doc/stunnel.8.in +++ b/doc/stunnel.8.in @@ -460,6 +460,13 @@ addresses specified with \fIcheckIP\fR. Multiple \fIcheckIP\fR options are allowed in a single service section. .Sp This option requires OpenSSL 1.0.2 or later. +.IP "\fBcheckPurpose\fR = default | any | client | server" 4 +.IX Item "\fBcheckPurpose\fR = default | any | client | server" +verify the Extended Key Usage of the peer certificate +.Sp +Certificate verification only succeeds if the certificate purpose, +specifically the Extended Key Usage, matches the parameters specified with +\fIcheckPurpose\fR. .IP "\fBciphers\fR = CIPHER_LIST" 4 .IX Item "ciphers = CIPHER_LIST" select permitted TLS ciphers (TLSv1.2 and below) diff --git a/doc/stunnel.html.in b/doc/stunnel.html.in index 90e8556..6eca48e 100644 --- a/doc/stunnel.html.in +++ b/doc/stunnel.html.in @@ -552,6 +552,14 @@ This option requires OpenSSL 1.0.2 or later. +</dd> +<dt id="checkPurpose-default-any-client-server">checkPurpose = default | any | client | server</dt> +<dd> + +verify the Extended Key Usage of the peer certificate + +Certificate verification only succeeds if the certificate purpose, specifically the Extended Key Usage, matches the parameters specified with checkPurpose. + </dd> <dt id="ciphers-CIPHER_LIST">ciphers = CIPHER_LIST</dt> <dd> diff --git a/doc/stunnel.pod.in b/doc/stunnel.pod.in index 752359d..977a879 100644 --- a/doc/stunnel.pod.in +++ b/doc/stunnel.pod.in @@ -500,6 +500,14 @@ Multiple I<checkIP> options are allowed in a single service section. This option requires OpenSSL 1.0.2 or later. +=item B<checkPurpose> = default | any | client | server + +verify the Extended Key Usage of the peer certificate + +Certificate verification only succeeds if the certificate purpose, +specifically the Extended Key Usage, matches the parameters specified with +I<checkPurpose>. + =item B<ciphers> = CIPHER_LIST select permitted TLS ciphers (TLSv1.2 and below) diff --git a/src/options.c b/src/options.c index 800d1f3..2ed4111 100644 --- a/src/options.c +++ b/src/options.c @@ -1854,6 +1854,41 @@ NOEXPORT const char *parse_service_option(CMD cmd, SERVICE_OPTIONS **section_ptr break; } + /* checkPurpose */ + switch(cmd) { + case CMD_SET_DEFAULTS: + section->check_purpose=X509_PURPOSE_DEFAULT_ANY; + break; + case CMD_SET_COPY: + section->check_purpose=new_service_options.check_purpose; + break; + case CMD_FREE: + break; + case CMD_SET_VALUE: + if(strcasecmp(opt, "checkPurpose")) + break; + if(!strcasecmp(arg, "default")) { + section->check_purpose=X509_PURPOSE_DEFAULT_ANY; + } else if(!strcasecmp(arg, "any")) { + section->check_purpose=X509_PURPOSE_ANY; + } else if(!strcasecmp(arg, "client")) { + section->check_purpose=X509_PURPOSE_SSL_CLIENT; + } else if(!strcasecmp(arg, "server")) { + section->check_purpose=X509_PURPOSE_SSL_SERVER; + } else { + return "The argument needs to be one of: default, any, client, server"; + } + return NULL; /* OK */ + case CMD_INITIALIZE: + break; + case CMD_PRINT_DEFAULTS: + break; + case CMD_PRINT_HELP: + s_log(LOG_NOTICE, "%-22s = client|server check for extended key usage", + "checkPurpose"); + break; + } + #endif /* OPENSSL_VERSION_NUMBER>=0x10002000L */ /* ciphers */ diff --git a/src/prototypes.h b/src/prototypes.h index 1142993..fde3da9 100644 --- a/src/prototypes.h +++ b/src/prototypes.h @@ -303,6 +303,7 @@ struct service_options_struct { NAME_LIST *check_host, *check_email, *check_ip; /* cert subject checks */ NAME_LIST *config; /* OpenSSL CONF options */ #endif /* OPENSSL_VERSION_NUMBER>=0x10002000L */ + int check_purpose; /* Extended Key Usage */ /* service-specific data for ctx.c */ char *cipher_list; diff --git a/src/verify.c b/src/verify.c index 7bab21e..e7dfe9f 100644 --- a/src/verify.c +++ b/src/verify.c @@ -78,6 +78,9 @@ int verify_init(SERVICE_OPTIONS *section) { verify_mode|=SSL_VERIFY_FAIL_IF_NO_PEER_CERT; } SSL_CTX_set_verify(section->ctx, verify_mode, verify_callback); + if(section->check_purpose) { + SSL_CTX_set_purpose(section->ctx, section->check_purpose); + } auth_warnings(section); -- 2.53.0

2 2

stunnel 5.78 released
by Michał Trojnara 10 Apr '26

10 Apr '26

Dear Users, I have released version 5.78 of stunnel. ### Version 5.78, 2026.04.09, urgency: MEDIUM * Security bugfixes - OpenSSL DLLs updated to version 3.5.6. * Bugfixes - Fixed WIN32 transfer() loop errors with OOB TCP. - Fixed a memory leak introduced in version 5.73. - Build fix for systems without timegm() (thanks to Jose A. Diaz and Shubham Gupta). - Fixed a startup crash when both global (default) and service-level lists of values are configured for an option. * Features - Support for zstd and brotli compression with OpenSSL 3.2 and TLS 1.2 or older. - WIN32 OpenSSL build with zlib and zstd support. - Support for new "options" parameter values. - Less bloated errors on an invalid configuration file. - Documentation updated from Pod to Pandoc Markdown. - Removed support for OpenSSL versions older than 0.9.8. The final update for the OpenSSL 0.9.7 branch (0.9.7m) was issed on 23 Feb 2007. Home page: https://www.stunnel.org/ Download: https://www.stunnel.org/downloads.html SHA-256 hashes: 8727e53bb8b7528f850327a2a149158422c02183bc120d1d733cc65b1e2c349d stunnel-5.78.tar.gz 541700197ce2e03dd86b343d9cbf6434359cca9f44e6927fde1d2c76c355c3e6 stunnel-5.78-win64-installer.exe b585d0828165d2e317f3956f2657fa6fb265b34b3ff49181bf561acd8eea2500 stunnel-5.78-android.zip Best regards, Mike

5 6

Connecting to Oracle errors to Connection reset by peer (104)
by HERCEK, Marián 27 Mar '26

27 Mar '26

Hello. Anybody has working setup with Oracle (SQLPlus)? Mine ends up with "Connection reset by peer". Server pid = /var/run/stunnel-oracle.pid cert = /etc/stunnel/stunnel.pem debug = 7 output = /var/log/stunnel/stunnel.log client = no [oracle] accept = 1.2.3.4:11521 connect = 127.0.0.1:1521 stunnel -version Initializing inetd mode configuration stunnel 5.71 on x86_64-redhat-linux-gnu platform Compiled/running with OpenSSL 1.1.1k FIPS 25 Mar 2021 Threading:PTHREAD Sockets:POLL,IPv6,SYSTEMD TLS:ENGINE,FIPS,OCSP,PSK,SNI Global options: fips = no RNDbytes = 1024 RNDfile = /dev/urandom RNDoverwrite = yes Service-level options: ciphers = PROFILE=SYSTEM (with "fips = yes") ciphers = PROFILE=SYSTEM (with "fips = no") ciphersuites = TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_CHACHA20_POLY1305_SHA256 (with TLSv1.3) curves = P-256:P-521:P-384 (with "fips = yes") curves = X25519:P-256:X448:P-521:P-384 (with "fips = no") debug = daemon.notice logId = sequential options = NO_SSLv2 options = NO_SSLv3 securityLevel = 2 sessionCacheSize = 1000 sessionCacheTimeout = 300 seconds stack = 65536 bytes TIMEOUTbusy = 300 seconds TIMEOUTclose = 60 seconds TIMEOUTconnect = 10 seconds TIMEOUTidle = 43200 seconds TIMEOUTocsp = 5 seconds verify = none Client debug = 7 output = stunnel.log client = yes [oracle] accept = 127.0.0.1:50102 connect = 1.2.3.4:11521 verifyChain = no stunnel 5.77 on x64-pc-mingw32-gnu platform Compiled/running with OpenSSL 3.5.5 27 Jan 2026 Threading:WIN32 Sockets:SELECT,IPv6 TLS:ENGINE,FIPS,OCSP,PSK,SNI Global options: fips = no RNDbytes = 1024 RNDoverwrite = yes taskbar = yes Service-level options: ciphers = FIPS:!DH:!kDHEPSK (with "fips = yes") ciphers = HIGH:!aNULL:!SSLv2:!DH:!kDHEPSK (with "fips = no") ciphersuites = TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_CHACHA20_POLY1305_SHA256 (with TLSv1.3) curves = P-256:P-521:P-384 (with "fips = yes") curves = X25519MLKEM768:X25519:P-256:X448:P-521:P-384 (with "fips = no") debug = notice logId = sequential options = NO_SSLv2 options = NO_SSLv3 securityLevel = 2 sessionCacheSize = 1000 sessionCacheTimeout = 300 seconds stack = 131072 bytes TIMEOUTbusy = 300 seconds TIMEOUTclose = 60 seconds TIMEOUTconnect = 10 seconds TIMEOUTidle = 43200 seconds TIMEOUTocsp = 5 seconds verify = none Debug logs from server (client logs are similar) 2026.03.26 12:54:18 LOG7[main]: Found 1 ready file descriptor(s) 2026.03.26 12:54:18 LOG7[main]: FD=4 events=0x2001 revents=0x0 2026.03.26 12:54:18 LOG7[main]: FD=9 events=0x2001 revents=0x1 2026.03.26 12:54:18 LOG7[main]: Service [oracle] accepted (FD=3) from 4.5.6.7:54017 2026.03.26 12:54:18 LOG7[3]: Service [oracle] started 2026.03.26 12:54:18 LOG7[3]: Setting local socket options (FD=3) 2026.03.26 12:54:18 LOG7[3]: Option TCP_NODELAY set on local socket 2026.03.26 12:54:18 LOG5[3]: Service [oracle] accepted connection from 4.5.6.7:54017 2026.03.26 12:54:18 LOG6[3]: Peer certificate not required 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): before SSL initialization 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): before SSL initialization 2026.03.26 12:54:18 LOG7[3]: Initializing application specific data for session authenticated 2026.03.26 12:54:18 LOG7[3]: Decrypt session ticket callback 2026.03.26 12:54:18 LOG6[3]: Decrypted ticket for an authenticated session: yes 2026.03.26 12:54:18 LOG7[3]: SNI: no virtual services defined 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS read client hello 2026.03.26 12:54:18 LOG7[3]: Deallocating application specific data for session connect address 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS write server hello 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS write change cipher spec 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): TLSv1.3 early data 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): TLSv1.3 early data 2026.03.26 12:54:18 LOG7[3]: Initializing application specific data for session authenticated 2026.03.26 12:54:18 LOG7[3]: Decrypt session ticket callback 2026.03.26 12:54:18 LOG6[3]: Decrypted ticket for an authenticated session: yes 2026.03.26 12:54:18 LOG7[3]: SNI: no virtual services defined 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS read client hello 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS write server hello 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): TLSv1.3 write encrypted extensions 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS write finished 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): TLSv1.3 early data 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): TLSv1.3 early data 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS read finished 2026.03.26 12:54:18 LOG7[3]: 4 server accept(s) requested 2026.03.26 12:54:18 LOG7[3]: 4 server accept(s) succeeded 2026.03.26 12:54:18 LOG7[3]: 0 server renegotiation(s) requested 2026.03.26 12:54:18 LOG7[3]: 2 session reuse(s) 2026.03.26 12:54:18 LOG7[3]: 3 internal session cache item(s) 2026.03.26 12:54:18 LOG7[3]: 0 internal session cache fill-up(s) 2026.03.26 12:54:18 LOG7[3]: 0 internal session cache miss(es) 2026.03.26 12:54:18 LOG7[3]: 0 external session cache hit(s) 2026.03.26 12:54:18 LOG7[3]: 0 expired session(s) retrieved 2026.03.26 12:54:18 LOG7[3]: Initializing application specific data for session authenticated 2026.03.26 12:54:18 LOG7[3]: Deallocating application specific data for session connect address 2026.03.26 12:54:18 LOG7[3]: Generate session ticket callback 2026.03.26 12:54:18 LOG7[3]: Initializing application specific data for session authenticated 2026.03.26 12:54:18 LOG7[3]: Deallocating application specific data for session connect address 2026.03.26 12:54:18 LOG7[3]: New session callback 2026.03.26 12:54:18 LOG6[3]: No peer certificate received 2026.03.26 12:54:18 LOG6[3]: Session id: 483B0F9A7D229A299E5FE0AF18B9BC00D26CFB781A363ABC612E6C8481EE8D11 2026.03.26 12:54:18 LOG7[3]: TLS state (accept): SSLv3/TLS write session ticket 2026.03.26 12:54:18 LOG6[3]: TLS accepted: previous session reused 2026.03.26 12:54:18 LOG6[3]: TLSv1.3 ciphersuite: TLS_AES_256_GCM_SHA384 (256-bit encryption) 2026.03.26 12:54:18 LOG6[3]: Peer temporary key: X25519, 253 bits 2026.03.26 12:54:18 LOG7[3]: Compression: null, expansion: null 2026.03.26 12:54:18 LOG6[3]: Session id: 483B0F9A7D229A299E5FE0AF18B9BC00D26CFB781A363ABC612E6C8481EE8D11 2026.03.26 12:54:18 LOG6[3]: s_connect: connecting 127.0.0.1:1521 2026.03.26 12:54:18 LOG7[3]: s_connect: s_poll_wait 127.0.0.1:1521: waiting 10 seconds 2026.03.26 12:54:18 LOG7[3]: FD=6 events=0x2001 revents=0x0 2026.03.26 12:54:18 LOG7[3]: FD=11 events=0x2005 revents=0x1 2026.03.26 12:54:18 LOG5[3]: s_connect: connected 127.0.0.1:1521 2026.03.26 12:54:18 LOG6[3]: persistence: 127.0.0.1:1521 cached 2026.03.26 12:54:18 LOG5[3]: Service [oracle] connected remote server from 127.0.0.1:43694 2026.03.26 12:54:18 LOG7[3]: Setting remote socket options (FD=11) 2026.03.26 12:54:18 LOG7[3]: Option TCP_NODELAY set on remote socket 2026.03.26 12:54:18 LOG7[3]: Remote descriptor (FD=11) initialized 2026.03.26 12:54:18 LOG6[3]: TLS fd: Connection reset by peer (104) 2026.03.26 12:54:18 LOG6[3]: transfer: SSL_read: Socket is closed 2026.03.26 12:54:18 LOG6[3]: TLS socket closed (SSL_read) 2026.03.26 12:54:18 LOG7[3]: Sent socket write shutdown 2026.03.26 12:54:18 LOG5[3]: Connection closed: 190 byte(s) sent to TLS, 663 byte(s) sent to socket 2026.03.26 12:54:18 LOG7[3]: Deallocating application specific data for session connect address 2026.03.26 12:54:18 LOG7[3]: Remote descriptor (FD=11) closed 2026.03.26 12:54:18 LOG7[3]: Local descriptor (FD=3) closed 2026.03.26 12:54:18 LOG7[3]: Service [oracle] finished (0 left)

2 1

stunnel 5.76+ segfaults when CAfile/cert are specified
by George Pucea 11 Mar '26

11 Mar '26

Dear team, I'm getting segfault when starting a stunnel. Here is a script to reproduce it with alpine: incident_cf cat stunnel-segfault-crash.sh *#!/bin/bash* *#* *# Reproducer: stunnel 5.76+ segfaults when CAfile/cert are specified* *# both globally and per-section with identical values.* *#* *# Requirements: Docker* *#* *# Expected output:* *# Segmentation fault* *# Exit: 139* *#* *docker run --rm alpine:latest sh -c '* *apk add -q stunnel openssl &&* *mkdir -p /app/managed &&* *openssl req -x509 -newkey rsa:2048 -keyout /tmp/k.pem -out /tmp/c.pem -days 1 -noenc -subj /CN=test 2>/dev/null &&* *cat /tmp/c.pem /tmp/k.pem > /app/managed/cert.pem &&* *cp /tmp/c.pem /app/managed/ca-file.pem &&* *echo "stunnel version: $(stunnel -version 2>&1 | grep "^stunnel")" &&* *printf "foreground=yes\nverify=2\nCApath=/etc/ssl/certs\nCAfile=/app/managed/ca-file.pem\ncert=/app/managed/cert.pem\npid=/tmp/s.pid\n[c0]\nclient=yes\naccept=33195\nCAfile=/app/managed/ca-file.pem\ncert=/app/managed/cert.pem\nconnect=192.0.2.1:12195 <http://192.0.2.1:12195>\n" > /tmp/test.conf &&* *stunnel /tmp/test.conf 2>&1; echo "Exit: $?"* *'* The workaround *is* removing the per-section CAfile/cert (relying on global values). Is this a known bug? Where can I report it? Thanks!

2 1

Systemd journal log line issues
by u34＠net9.cf 05 Mar '26

05 Mar '26

This messgave could be related to the [systemd and stunnel.service](https://www.stunnel.org/mailman3/hyperkitty/list/stunnel-u… thread. With stunnel 5.77 from the official Debian package, and using instances of Debian systemd template, I am getting duplicate lines at the journal. Each line is duplicated, as in Mar 03 01:02:24 myhost stunnel[50237]: LOG5[ui]: Log file reopened Mar 03 01:02:24 myhost stunnel4[50237]: 2026.03.03 01:02:24 LOG5[ui]: Log file reopened The order of those lines can be reversed in the sense that the line with the duplicate date sometimes appears before the other line. As an aside, the manual page states -reopen (Windows NT and later only) Reopen the log file of the running NT Service but this report is for a Linux machine. Am I confusing what the manual page states for a command line option with the fact that stunnel reopens the log file periodicaly on all platforms? In addition to my possible misunderstanding about the log file being reopened, I find it odd there is a log file mentioned at all. Because I didn't configured a log file in the configuration file at all. Returning to the duplicate lines issue, I have tried to run stunnel directly from the command line, as in # /usr/bin/stunnel /etc/stunnel/stunnel.conf & With this command line, I got log messages in the terminal, as well as in systemd journal. Can it be that when run by the systemd template, the lines from the terminal are directed to the journal, and that explain the duplication?

2 1

SSL handshake failure
by Jean-Luc Deschamps Berger 03 Mar '26

03 Mar '26

Hi, I have an issue with one connection using stunnel as client. The purpose is to connect to a server on port 8443. The connection works on the first request. But the second one is always rejected. In the log, I see on the second connection, an attempt to resume and then a handshake failure. I have tried some different parameters sslVersion, options... but with still the same issue. As there is no performance issue on this connection, is there any parameter that can stop the resume attempt ? See below the configuration file and traces of first request (Ok) and second request (NotOK). Thanks by advance for your help. Best regards Jean-Luc DESCHAMPS BERGER stunnel.conf ------------------------------------------------------ client = yes output = /GPTO/CCTMP/stunnel.log debug = 7 [olt] accept = localhost:8443 connect = 10.75.1.6:8443 verifyChain = no sslVersion = TLSv1.2 options = NO_SSLv2 options = NO_SSLv3 First connection: OK ------------------------------------------------------------------ 2026.03.04 02:00:02 LOG5[0]: Service [olt] accepted connection from 127.0.0.1:58704 2026.03.04 02:00:02 LOG6[0]: s_connect: connecting 10.75.1.6:8443 2026.03.04 02:00:02 LOG7[0]: s_connect: s_poll_wait 10.75.1.6:8443: waiting 10 seconds 2026.03.04 02:00:02 LOG7[0]: FD=6 events=0x2001 revents=0x0 2026.03.04 02:00:02 LOG7[0]: FD=15 events=0x2005 revents=0x0 2026.03.04 02:00:02 LOG5[0]: s_connect: connected 10.75.1.6:8443 2026.03.04 02:00:02 LOG5[0]: Service [olt] connected remote server from 192.168.16.249:42547 2026.03.04 02:00:02 LOG7[0]: Setting remote socket options (FD=15) 2026.03.04 02:00:02 LOG7[0]: Option TCP_NODELAY set on remote socket 2026.03.04 02:00:02 LOG7[0]: Remote descriptor (FD=15) initialized 2026.03.04 02:00:02 LOG6[0]: SNI: sending servername: 10.75.1.6 2026.03.04 02:00:02 LOG7[0]: No previous session to resume 2026.03.04 02:00:02 LOG6[0]: Peer certificate not required 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): before/connect initialization 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 write client hello A 2026.03.04 02:00:02 LOG7[0]: OCSP stapling: Client callback called 2026.03.04 02:00:02 LOG6[0]: OCSP: Certificate chain verification disabled 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 read server hello A 2026.03.04 02:00:02 LOG6[0]: CERT: Certificate verification disabled 2026.03.04 02:00:02 LOG6[0]: CERT: Certificate verification disabled 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 read server certificate A 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 read server key exchange A 2026.03.04 02:00:02 LOG6[0]: Client certificate not requested 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 read server done A 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 write client key exchange A 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 write change cipher spec A 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 write finished A 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 flush data 2026.03.04 02:00:02 LOG7[0]: TLS state (connect): SSLv3 read finished A 2026.03.04 02:00:02 LOG7[0]: New session callback 2026.03.04 02:00:02 LOG7[0]: Peer certificate was cached (1241 bytes) 2026.03.04 02:00:02 LOG6[0]: Session id: A8CFAD0D0E7D060D56EFF5045F8E1570727951423AB00D7CF70B4E4423396293 2026.03.04 02:00:02 LOG7[0]: 1 client connect(s) requested 2026.03.04 02:00:02 LOG7[0]: 1 client connect(s) succeeded 2026.03.04 02:00:02 LOG7[0]: 0 client renegotiation(s) requested 2026.03.04 02:00:02 LOG7[0]: 0 session reuse(s) 2026.03.04 02:00:02 LOG6[0]: TLS connected: new session negotiated 2026.03.04 02:00:02 LOG6[0]: TLSv1.2 ciphersuite: ECDHE-RSA-AES256-GCM-SHA384 (256-bit encryption) 2026.03.04 02:00:02 LOG7[0]: Compression: null, expansion: null 2026.03.04 02:00:02 LOG6[0]: Read socket closed (readsocket) 2026.03.04 02:00:02 LOG7[0]: Sending close_notify alert 2026.03.04 02:00:02 LOG7[0]: TLS alert (write): warning: close notify 2026.03.04 02:00:02 LOG6[0]: SSL_shutdown successfully sent close_notify alert 2026.03.04 02:00:02 LOG6[0]: transfer: SSL_read: Socket is closed 2026.03.04 02:00:02 LOG6[0]: TLS socket closed (SSL_read) 2026.03.04 02:00:02 LOG7[0]: Sent socket write shutdown 2026.03.04 02:00:02 LOG5[0]: Connection closed: 593 byte(s) sent to TLS, 704 byte(s) sent to socket Second connection: notOK ------------------------------------------------------------------------------------------------------------- 2026.03.04 02:00:04 LOG5[1]: Service [olt] accepted connection from 127.0.0.1:58710 2026.03.04 02:00:04 LOG6[1]: s_connect: connecting 10.75.1.6:8443 2026.03.04 02:00:04 LOG7[1]: s_connect: s_poll_wait 10.75.1.6:8443: waiting 10 seconds 2026.03.04 02:00:04 LOG7[1]: FD=6 events=0x2001 revents=0x0 2026.03.04 02:00:04 LOG7[1]: FD=15 events=0x2005 revents=0x0 2026.03.04 02:00:04 LOG5[1]: s_connect: connected 10.75.1.6:8443 2026.03.04 02:00:04 LOG5[1]: Service [olt] connected remote server from 192.168.16.249:42553 2026.03.04 02:00:04 LOG7[1]: Setting remote socket options (FD=15) 2026.03.04 02:00:04 LOG7[1]: Option TCP_NODELAY set on remote socket 2026.03.04 02:00:04 LOG7[1]: Remote descriptor (FD=15) initialized 2026.03.04 02:00:04 LOG6[1]: SNI: sending servername: 10.75.1.6 2026.03.04 02:00:04 LOG6[1]: Attempting to resume: A8CFAD0D0E7D060D56EFF5045F8E1570727951423AB00D7CF70B4E4423396293 2026.03.04 02:00:04 LOG6[1]: Peer certificate not required 2026.03.04 02:00:04 LOG7[1]: TLS state (connect): before/connect initialization 2026.03.04 02:00:04 LOG7[1]: TLS state (connect): SSLv3 write client hello A 2026.03.04 02:00:04 LOG7[1]: TLS alert (read): fatal: handshake failure 2026.03.04 02:00:04 LOG3[1]: SSL_connect: s3_pkt.c:1259: error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure: client 127.0.0.1:58710 2026.03.04 02:00:04 LOG5[1]: Connection closed/reset: 0 byte(s) sent to TLS, 0 byte(s) sent to socket 2026.03.04 02:00:04 LOG7[1]: Remote descriptor (FD=15) closed 2026.03.04 02:00:04 LOG7[1]: local_rfd/local_wfd reset (FD=3) 2026.03.04 02:00:04 LOG7[1]: Local descriptor (FD=3) closed 2026.03.04 02:00:04 LOG7[1]: Service [olt] finished (0 left)

1 0

How to use static DH parameters?
by Ian Pilcher 28 Feb '26

28 Feb '26

I am trying to configure stunnel to use static DH parameters. The man page says: Alternatively, it is possible to specify static DH parameters in the certificate file, which disables generating temporary DH parameters: openssl dhparam 2048 >> stunnel.pem But, I'm not 100% clear on what certificate file it is talking about. My configuration looks like this. [switch2-frontend] accept = 0.0.0.0:8402 CAfile = /etc/ipa/ca.crt cert = /etc/pki/tls/certs/stunnel/switch2.crt key = /tmp/keys/switch2.key connect = 127.255.255.254:8082 [switch2-backend] client = yes accept = 127.255.255.254:8082 connect = 172.31.4.2:443 verifyChain = yes checkHost = switch2.penurio.us CAfile = /etc/pki/tls/certs/stunnel/switch-ca.crt sslVersion = TLSv1 ciphers = DHE-RSA-AES256-SHA options = ALLOW_UNSAFE_LEGACY_RENEGOTIATION securityLevel = 0 OCSPrequire = no OCSPaia = no Would I add the DH parameters to /etc/pki/tls/certs/stunnel/switch2.crt? Thanks! -- ======================================================================== If your user interface is intuitive in retrospect ... it isn't intuitive ========================================================================

2 1

List server change
by Michał Trojnara 28 Feb '26

28 Feb '26

Dear users, The list address has been changed from stunnel-users(a)stunnel.org to stunnel-users(a)lists.stunnel.org. Please let me know if you experience any issues caused by this change. Best regards, Mike

1 0

Fwd: timegm not supported in AIX
by shubham gupta 26 Feb '26

26 Feb '26

Hi, Sorry for the wrong patch. I have attached the corrected one in this email. Thanks, Shubham ---------- Forwarded message --------- From: shubham gupta <shubham17031994(a)gmail.com> Date: Thu, Feb 26, 2026 at 2:55 PM Subject: timegm not supported in AIX To: <stunnel-users(a)stunnel.org> Hi, I am building the latest stunnel on an AIX machine. However I see build failure due to missing API timegm. Snippet from the error generating file src/oscp.c #ifdef _WIN32 return _mkgmtime(&tm); #else /* defined _WIN32 */ return timegm(&tm); #endif /* defined _WIN32 */ Error log: libtool: link: /opt/freeware/bin/gcc -maix64 -O2 -DOPENSSL_NO_PSK -g -O2 -Wall -Wextra -Wpedantic -Wformat=2 -Wconversion -Wno-deprecated-declarations -Wno-unused-command-line-argument -fPIE -D_FORTIFY_SOURCE=2 -Wl,-blibpath:/opt/freeware/lib64:/opt/freeware/lib:/usr/lib:/lib -fPIE -pie -o stunnel stunnel-tls.o stunnel-str.o stunnel-file.o stunnel-client.o stunnel-log.o stunnel-options.o stunnel-protocol.o stunnel-network.o stunnel-resolver.o stunnel-ssl.o stunnel-ctx.o stunnel-verify.o stunnel-sthreads.o stunnel-ocsp.o stunnel-fd.o stunnel-dhparam.o stunnel-cron.o stunnel-stunnel.o stunnel-pty.o stunnel-libwrap.o stunnel-ui_unix.o -L/usr/lib -lssl -lcrypto -L/opt/freeware/lib64 -L/opt/freeware/lib -lpthread ld: 0711-317 ERROR: Undefined symbol: .timegm Please consider the patch attached along with the email for fixing the issue. Thanks, Shubham [image: Mailsuite] Email tracked with Mailsuite · Opt out <https://u.list-prefs.com/en/privacy/opt-out/unsubscribe/906ba64869a1f2284b6…> 26/02/26, 14:51:51

2 2

systemd and stunnel.service
by Mike 25 Feb '26

25 Feb '26

I'm setting up a new ubuntu server and it includes stunnel version 5.74. My ultimate goal is to have the service managed by systemd. Things didn't really work out of the box because of the needed configuration file which I was able to use from an existing didn't have the appropriate information in it. So, even though it would start (using initd), when I would try to stop it, it wouldn't. This turned out to be pretty straightforward solve by adding the following to my one and only conf file: setuid = stunnel4 setgid = stunnel4 ; PID file is created inside the chroot jail (if enabled) pid = /var/run/stunnel4/stunnel4.pid While the example file in /usr/share/doc/stunnel4/examples/stunnel.conf-sample had these entries in the file, they were commented out and I wasn't sure if that those were actual defaults, or needed to be uncommented for production. The later seemed to be the case. After fixing that, I was able to use systemctl start/stop as normal, however I noticed that it was being started by the old initd setup. #system status stunnel4 ● stunnel4.service - LSB: Start or stop stunnel 4.x (TLS tunnel for network daemons) Loaded: loaded (/etc/init.d/stunnel4; generated) Active: active (running) since Tue 2026-02-24 20:35:35 CST; 2s ago Invocation: 343fad33bfb949aa8b48285e37c7f05a Docs: man:systemd-sysv-generator(8) Process: 4754 ExecStart=/etc/init.d/stunnel4 start (code=exited, status=0/SUCCESS) Tasks: 4 (limit: 4367) CPU: 192ms CGroup: /system.slice/stunnel4.service So after further searching I found the following files: /usr/lib/systemd/system/stunnel.target /usr/lib/systemd/system/[email protected] I executed the command: systemctl enable stunnel@myconffile When I use this command: systemctl start stunnel@myconffile It definitely executes the correct command, but then the whole service shuts down and I get this: ○ stunnel(a)myconffile.service - TLS tunnel for network daemons - per-config-file service Loaded: loaded (/etc/systemd/system/[email protected]; enabled; preset: enabled) Active: inactive (dead) since Tue 2026-02-24 20:44:54 CST; 11s ago Duration: 20.157s Invocation: 46cddb34062b401b87e8516f47b1482b Docs: man:stunnel4(8) Process: 5099 ExecStart=/usr/bin/stunnel4 /etc/stunnel/attuverse.conf (code=exited, status=0/SUCCESS) Main PID: 5099 (code=exited, status=0/SUCCESS) CPU: 128ms No stunnel service is running. There wasn't anything in the log that I could find that would indicate why it stopped. if I execute this command: /usr/bin/stunnel4 /etc/stunnel/myconffile.conf It works how I would expect it to. For now I'm using the initd initialization, but I would love to get the systemd version running. Anyone have some suggestions? Thanks. Mike

4 13

Question on 5.77 found differences.
by Michael D. Setzer II 18 Feb '26

18 Feb '26

Did the configure and make and then make install, but it didn't work as it had on 5.76 since it was saying stunnel.conf was in wrong place?? Had always had in /etc/stunnel/stunnel.conf with both the fedora version and the 5.76 binary files in ls /usr/local/bin/stunnel* -l 796752 Feb 18 13:20 /usr/local/bin/stunnel 2793 Feb 18 13:20 /usr/local/bin/stunnel3 792448 Feb 18 13:19 /usr/local/bin/stunnel-5.76 For 5.77 had to copy stunnel.conf /usr/local/etc/stunnel/stunnel.conf Had just done ./configure make make install stunnel -version Initializing inetd mode configuration stunnel 5.77 on x86_64-pc-linux-gnu platform Compiled/running with OpenSSL 3.2.6 30 Sep 2025 Threading:PTHREAD Sockets:POLL,IPv6,SYSTEMD TLS:FIPS,OCSP,PSK,SNI Global options: fips = no RNDbytes = 1024 RNDfile = /dev/urandom RNDoverwrite = yes Service-level options: ciphers = FIPS:!DH:!kDHEPSK (with "fips = yes") ciphers = HIGH:!aNULL:!SSLv2:!DH:!kDHEPSK (with "fips = no") ciphersuites = TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_C HACHA20_POLY1305_SHA256 (with TLSv1.3) curves = P-256:P-521:P-384 (with "fips = yes") curves = X25519:P-256:X448:P-521:P-384 (with "fips = no") debug = daemon.notice logId = sequential options = NO_SSLv2 options = NO_SSLv3 securityLevel = 2 sessionCacheSize = 1000 sessionCacheTimeout = 300 seconds stack = 131072 bytes TIMEOUTbusy = 300 seconds TIMEOUTclose = 60 seconds TIMEOUTconnect = 10 seconds TIMEOUTidle = 43200 seconds TIMEOUTocsp = 5 seconds verify = none Ports shows: # lsof -i | grep stunnel stunnel 171807 nobody 9u IPv4 388014 0t0 TCP localhost:20995 (LISTEN) stunnel 171807 nobody 10u IPv4 388015 0t0 TCP localhost:20465 (LISTEN) stunnel 171807 nobody 11u IPv4 388016 0t0 TCP localhost:20993 (LISTEN) stunnel 171807 nobody 12u IPv4 388017 0t0 TCP localhost:20996 (LISTEN) stunnel 171807 nobody 13u IPv4 388018 0t0 TCP localhost:20466 (LISTEN) stunnel 171807 nobody 14u IPv4 388019 0t0 TCP localhost:10995 (LISTEN) stunnel 171807 nobody 15u IPv4 388020 0t0 TCP localhost:10465 (LISTEN) So, all seems fine, but not clear on why location of stunnel.conf changed. Another thing tried to look at donate option and goes to this page https://business.revolut.com/revolutme/mobicompolska But shows. User not found Use for my personal setup with Pegasus Email to 3 ISPs, but was looking to give something. Thanks. Using Fedora 42 and 43 systems, but now using the stunnel.org setup instead of fedora's repos version. +------------------------------------------------------------+ Michael D. Setzer II - Computer Science Instructor (Retired) mailto:[email protected] mailto:[email protected] mailto:[email protected] Guam - Where America's Day Begins G4L Disk Imaging Project maintainer http://sourceforge.net/projects/g4l/ +------------------------------------------------------------+

1 0

stunnel 5.77 released
by Michał Trojnara 17 Feb '26

17 Feb '26

Dear Users, I have released version 5.77 of stunnel. ### Version 5.77, 2026.02.17, urgency: MEDIUM * Security bugfixes - OpenSSL DLLs updated to version 3.5.5. * Bugfixes - Avoid attempting to fetch OCSP stapling for PSK-only configuration sections. * Features - Merged applicable patches from Fedora and Debian: - Use SOURCE_DATE_EPOCH for reproducible builds. - Skip the OpenSSL version check when AUTOPKGTEST_TMP is set. - Enable PrivateTmp in the stunnel.service template. - Clarify the manual page for the "curves" option. - Log client IP addresses on TLS errors. Home page: https://www.stunnel.org/ Download: https://www.stunnel.org/downloads.html SHA-256 hashes: ec026f4fae4e0d25b940cc7a9451d925e359e7fd59e9edad20baea66ce45f263 stunnel-5.77.tar.gz 59ba0c5330de85ef474164b40cc559b2eb4e2b8d788c48b564e2257efa236384 stunnel-5.77-win64-installer.exe 718431a1d3c889806b61d6f082bbfaaa29529ce422d8115ad2211574dfb89ec1 stunnel-5.77-android.zip Best regards, Mike

1 0

Question on trying to setup stunnel 5.76 on Fedora 42/43 system.
by Michael D. Setzer II 13 Feb '26

13 Feb '26

Run into some issues with trying to upgrade the stunnel to 5.76 version while Fedora repos version is still at 5.75. Found one thing that showed using this configurations options. ./configure \ --sysconfdir=/etc \ --localstatedir=/var \ --enable-systemd \ --with-ssl=/usr But using it, the stunnel 5.76 is still installing in /usr/local/bin? Also, finding the systemctl status stunnel is still showing the /usr/bin/stunnel 5.75 being run? Removed the fedora repo version, and then systemctl no longer shows a service for stunnel, but run it manually at boot, and it works fine. Seems the fedora version has a ENGINE option that the stunnel option doesn't. stunnel -version Initializing inetd mode configuration stunnel 5.76 on x86_64-pc-linux-gnu platform Compiled/running with OpenSSL 3.2.6 30 Sep 2025 Threading:PTHREAD Sockets:POLL,IPv6,SYSTEMD TLS:FIPS,OCSP,PSK,SNI Global options: fips = no RNDbytes = 1024 RNDfile = /dev/urandom RNDoverwrite = yes Service-level options: ciphers = FIPS:!DH:!kDHEPSK (with "fips = yes") ciphers = HIGH:!aNULL:!SSLv2:!DH:!kDHEPSK (with "fips = no") ciphersuites = TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_C HACHA20_POLY1305_SHA256 (with TLSv1.3) curves = P-256:P-521:P-384 (with "fips = yes") curves = X25519:P-256:X448:P-521:P-384 (with "fips = no") debug = daemon.notice logId = sequential options = NO_SSLv2 options = NO_SSLv3 securityLevel = 2 sessionCacheSize = 1000 sessionCacheTimeout = 300 seconds stack = 131072 bytes TIMEOUTbusy = 300 seconds TIMEOUTclose = 60 seconds TIMEOUTconnect = 10 seconds TIMEOUTidle = 43200 seconds TIMEOUTocsp = 5 seconds verify = none Know that sometmes the fedora repo doesn't update each time, or it takes more time? Is there way to install the latest version and have the systemd setup to work. At present, have the Fedora repo version uninstalled, and run the stunnel in rc.local? Thanks. +------------------------------------------------------------+ Michael D. Setzer II - Computer Science Instructor (Retired) mailto:[email protected] mailto:[email protected] mailto:[email protected] Guam - Where America's Day Begins G4L Disk Imaging Project maintainer http://sourceforge.net/projects/g4l/ +------------------------------------------------------------+

2 2

Rare crashes of stunnel
by Don Lee 07 Feb '26

07 Feb '26

Hi guys, I have been running stunnel in production for my email server users. It’s been great. It’s pretty stable, and does all that I ned to allow my users to connect to my ancient mailserver (EIMS) with modern SSL. In fact, it’s been so stable that until recently I had no backup on stunnel It just ran. Unfortunately, I have had some incidents where stunnel just crashes. When it does, it looks like my email facilities are completely down - not good. I now have a script that monitors stunnel, and when stunnel dies, the script re-starts it. Below is a snippet of my stunnel log at the crash point. Does anyone else have this problem? Are the developers interested in my data? I installed it as a pre-built binary package, and this is the most recent version in the packages collection, so I am reluctant to build my own stunnel. Thank you for a great tool. -dgl- 2026.02.06 15:04:25 LOG5[75312]: Connection closed: 784 byte(s) sent to TLS, 224 byte(s) sent to socket 2026.02.06 15:04:25 LOG5[75311]: Connection closed: 2036 byte(s) sent to TLS, 22 9 byte(s) sent to socket 2026.02.06 15:04:25 LOG5[75313]: Service [imaps] accepted connection from 107.12 3.20.177:6908 2026.02.06 15:04:25 LOG5[75314]: Service [imaps] accepted connection from 107.12 3.20.177:9568 2026.02.06 15:04:25 LOG5[75313]: s_connect: connected 71.39.101.34:143 2026.02.06 15:04:25 LOG5[75313]: Service [imaps] connected remote server from 71 .39.101.39:49527 2026.02.06 15:04:25 LOG5[75314]: s_connect: connected 71.39.101.34:143 2026.02.06 15:04:25 LOG5[75314]: Service [imaps] connected remote server from 71 .39.101.39:49526 2026.02.06 15:04:28 LOG3[per-minute]: OCSP: OCSP_check_validity: /usr/src/crypto /external/bsd/openssl/dist/crypto/ocsp/ocsp_cl.c:378: error:2707307D:OCSP routin es:OCSP_check_validity:status expired 2026.02.06 15:04:28 LOG4[per-minute]: OCSP: Unknown verification status INTERNAL ERROR: Memory allocated in a different thread at ocsp.c, line 412 2026.02.06 15:04:41 LOG5[ui]: stunnel 5.73 on x86_64--netbsd platform 2026.02.06 15:04:41 LOG5[ui]: Compiled/running with OpenSSL 1.1.1t 7 Feb 2023 2026.02.06 15:04:41 LOG5[ui]: Threading:PTHREAD Sockets:POLL,IPv6 TLS:ENGINE,OCS P,PSK,SNI Auth:LIBWRAP 2026.02.06 15:04:41 LOG5[ui]: Reading configuration from file /usr/pkg/etc/stunn el/stunnel.conf 2026.02.06 15:04:41 LOG5[ui]: UTF-8 byte order mark detected 2026.02.06 15:04:41 LOG5[ui]: OCSP: Connecting the AIA responder "http://status. rapidssl.com"

2 1

CoAP protocol support
by James Hanley 30 Jan '26

30 Jan '26

I’m not sure if this is the right forum but adding CoAP/CoAP support analogous to http/https but for both TCP/TLS & UDP/DTLS would be useful for testing. -Jim

2 1

Re: stunnel : SSL_connect: Peer suddenly disconnected
by Jose Alf. 19 Dec '25

19 Dec '25

Hi Souheila, Are you sure that you are running an NFS server in your azure machine that natively supports TLS? If you are not, you must put an stunnel wrapper in front of it. It looks to me that the NFS service exposed at 52.239.241.136:2049 does not support TLS. 2025.12.19 07:53:48 LOG7[0]: Service [52.239.241.136] started 2025.12.19 07:53:48 LOG7[0]: Setting local socket options (FD=584) 2025.12.19 07:53:48 LOG7[0]: Option TCP_NODELAY set on local socket 2025.12.19 07:53:48 LOG5[0]: Service [52.239.241.136] accepted connection from 127.0.0.1:58887 2025.12.19 07:53:48 LOG6[0]: s_connect: connecting 52.239.241.136:2049 2025.12.19 07:53:48 LOG7[0]: s_connect: s_poll_wait 52.239.241.136:2049: waiting 10 seconds 2025.12.19 07:53:48 LOG7[0]: FD=1040 ifds=rwx ofds=--- 2025.12.19 07:53:49 LOG5[0]: s_connect: connected 52.239.241.136:2049 2025.12.19 07:53:49 LOG5[0]: Service [52.239.241.136] connected remote server from 192.168.1.26:58888 2025.12.19 07:53:49 LOG7[0]: Setting remote socket options (FD=1040) 2025.12.19 07:53:49 LOG7[0]: Option TCP_NODELAY set on remote socket 2025.12.19 07:53:49 LOG7[0]: Remote descriptor (FD=1040) initialized 2025.12.19 07:53:49 LOG6[0]: SNI: sending servername: 52.239.241.136 2025.12.19 07:53:49 LOG7[0]: No previous session to resume 2025.12.19 07:53:49 LOG6[0]: Peer certificate not required 2025.12.19 07:53:49 LOG7[0]: TLS state (connect): before SSL initialization 2025.12.19 07:53:49 LOG7[0]: TLS state (connect): SSLv3/TLS write client hello 2025.12.19 07:53:49 LOG7[0]: TLS alert (write): fatal: decode error 2025.12.19 07:53:49 LOG3[0]: SSL_connect: ssl/record/rec_layer_s3.c:696: error:0A000126:SSL routines::unexpected eof while reading 2025.12.19 07:53:49 LOG5[0]: Connection closed/reset: 0 byte(s) sent to TLS, 0 byte(s) sent to socket 2025.12.19 07:53:49 LOG7[0]: Remote descriptor (FD=1040) closed 2025.12.19 07:53:49 LOG7[0]: local_rfd/local_wfd reset (FD=584) 2025.12.19 07:53:49 LOG7[0]: Local descriptor (FD=584) closed 2025.12.19 07:53:49 LOG7[0]: Service [52.239.241.136] finished (0 left) Regards,Jose A. Diaz On 18/12/2025, at 11:25 PM, Souheila Hechaichi via stunnel-users <stunnel-users(a)stunnel.org> wrote: Hey, I hope your help.The problem of 403754EAC87F0000:error:0A000126:SSL routines::unexpected eof while reading:../ssl/record/rec_layer_s3.c:696: is a bug in openssl version 3.x.xWhith my configuration OpenSSL 1.1.1f, the connection succeded but Its systematically closes <image.png> And with tcpdump I observe a connection reset<image.png>Best regards;From: Michał Trojnara via stunnel-users <stunnel-users(a)stunnel.org> Sent: Thursday, December 18, 2025 8:24 PM To: stunnel-users(a)stunnel.org <stunnel-users(a)stunnel.org> Subject: [stunnel-users] Re: stunnel : SSL_connect: Peer suddenly disconnected Hi Souheila, It does not look like your remote machine accepts TLS: $ openssl s_client -connect 52.239.241.136:2049 Connecting to 52.239.241.136 CONNECTED(00000003) 403754EAC87F0000:error:0A000126:SSL routines::unexpected eof while reading:../ssl/record/rec_layer_s3.c:696: Why exactly do you think that stunnel could be used to mount NFS file shares? Stunnel can be a TLS client, but not an NFS client. Those aredifferent protocols. Best regards, Mike On 12/18/25 6:15 PM, Souheila Hechaichi via stunnel-users wrote: I am using stunnel to mount an azure nfs file share. The stunnel process log the following messageDec 18 17:55:20 vmubuntu18 stunnel: LOG3[23840]: SSL_connect: Peer suddenly disconnected The stunnel configure file isverifyChain = nodebug = debugoutput = /etc/stunnel/microsoft/aznfs/nfsv4_fileShare/logs/stunnel_52.239.241.136.logpid = /etc/stunnel/microsoft/aznfs/nfsv4_fileShare/logs/stunnel_52.239.241.136.pidTIMEOUTidle = 61 [52.239.241.136]client = yesaccept = 127.0.0.1:20049connect = 52.239.241.136:2049 A trace with tcpdump display the following logs<image.png> We observe a reset connection between azure server and my machine. Best regardsSouheila _______________________________________________ stunnel-users mailing list -- stunnel-users(a)stunnel.org To unsubscribe send an email to stunnel-users-leave(a)stunnel.org _______________________________________________ stunnel-users mailing list -- stunnel-users(a)stunnel.org To unsubscribe send an email to stunnel-users-leave(a)stunnel.org

1 0

stunnel : SSL_connect: Peer suddenly disconnected
by Souheila Hechaichi 18 Dec '25

18 Dec '25

I am using stunnel to mount an azure nfs file share. The stunnel process log the following message Dec 18 17:55:20 vmubuntu18 stunnel: LOG3[23840]: SSL_connect: Peer suddenly disconnected The stunnel configure file is verifyChain = no debug = debug output = /etc/stunnel/microsoft/aznfs/nfsv4_fileShare/logs/stunnel_52.239.241.136.log pid = /etc/stunnel/microsoft/aznfs/nfsv4_fileShare/logs/stunnel_52.239.241.136.pid TIMEOUTidle = 61 [52.239.241.136] client = yes accept = 127.0.0.1:20049 connect = 52.239.241.136:2049 A trace with tcpdump display the following logs [cid:defde221-2fed-4b36-9480-0181f6f7d5a9] We observe a reset connection between azure server and my machine. Best regards Souheila

2 2

OCSPflag not processed in ocsp_stapling() ?
by King's Way 01 Dec '25

01 Dec '25

Hi there, I was trying to make stunnel ignore OCSP verification error for local certificates when doing OCSP Stapling. But it seems the flag "OCSPflag = NOVERIFY" is not properly passed to openssl. I have tried to patch it in function ocsp_stapling(), and it worked. But I wonder whether it is a bug or intentionally designed this way? With kind regards！ ------------------------------------------------------------ King's Way <io[AT]stdio.io<http://stdio.io>>

1 0

Getting Started - Unique Situation
by Kevin Morris 21 Nov '25

21 Nov '25

Hi All! About me: I've never heard of stunnel before but it sounds great. I'm not a networking/internet expert. Here is my situation: Platform: Microsoft Windows Server 2016. Two Network Interface Cards. Port 443 on both currently have HTTPS/TCP traffic on them, from two different Web Apps, each with their own domain. Everything is working properly, traffic is very low, only a few (about 20) hits per minute (each port) at max load. Both Web Apps are built using Lazarus, Free Pascal, Brook Framework. The Brook Framework has the built-in ability to handle SSL/TLS encryption. Certs are supplied by Let's Encrypt, and new certs are obtained by a bot. I now have a third and soon a forth Web App built using the same technology, but my only two 443 ports are occupied. Here is my requirement: I need something that will act as a "port splitter". Maybe this is also known as a reverse proxy. Example: Incoming URLs on port 443: https://mywebapp.companyname.com/bob/useraccount?act=login&exp=pg https://mywebapp.companyname.com/betty/useraccount?act=login&exp=pg The port splitter needs to recognize the part in teal green (maybe called an "entry point"?), and pass that unchanged traffic through to (and from) a port that the associated Web App is listening on. WebApp "bob" is listening on local port 449 (not exposed to the internet, only conversing with stunnel) WebApp "betty" is listening on local port 451 (not exposed to the internet, only conversing with stunnel) Both Web Apps will send/receive their own HTTPS traffic, handle their own decryption/encryption, and send it back through their respective listening ports, through the port splitter, back the the requesting user. No load balancing is required. No decryption/encryption/certs is/are required. This needs to happen downstream from our router, without making any changes to OS rules or router settings. I'd like to just shut down the current Web App listening on port 443, reconfig it to a new local port As I looked through the FAQ and manual, I could not determine if stunnel could do this. So my questions are: A) Can stunnel do this? B) If so, is there a "How To" I missed in the manual I can read to do this? C) If ((A = Yes) and B = No)), can you tell me in a couple sentences where to look in the config file to do some reading and get this set up? If we can get this working, there are other Lazarus/Brook developers who could benefit from using stunnel. If stunnel is not the answer, is there another "port splitter" piece of software that you know of that can? (other than IIS with ARR and WAP, I don't want to use those, I'm slowly trying to de-Microsoft my infrastructure.) Thanks in advance!

2 1

+=item B<requireCert> = yes | no ignored when client = yes
by u34＠net9.cf 13 Nov '25

13 Nov '25

In my opinion, the following emphasis worth including: --- stunnel.pod.in.orig 2025-10-07 19:50:30.097392645 +0000 +++ stunnel.pod.in.new 2025-10-07 20:25:54.448391940 +0000 @@ -1065,6 +1065,8 @@ =item B<requireCert> = yes | no +Ignored when client = yes. + require a client certificate for I<verifyChain> or I<verifyPeer> With I<requireCert> set to I<no>, the B<stunnel> server accepts client

2 1

stunnel 5.76 core dumped
by Bogdan Siara 02 Nov '25

02 Nov '25

Hi, I try to run stunnel with certs from hardware token and I get error: root@c6b200207f1a:/stunnel-5.76# stunnel free(): invalid pointer Aborted (core dumped) This is my configuration: engine = pkcs11 engineCtrl = MODULE_PATH:/usr/lib/libeToken.so engineCtrl = PIN:pin output = /var/log/stunnel.log debug=debug [in-hdt] client=no accept = 172.18.1.2:443 connect=127.0.0.1:8080 cert = /etc/stunnel/certs/hdt.pem key = /etc/stunnel/certs/hdt.key sessionResume = no options = NO_TICKET retry=yes TIMEOUTclose = 0 debug=debug [in-vpc] client=no accept = 172.18.2.2:443 connect=127.0.0.1:8081 cert = /etc/stunnel/certs/vpc.pem key = /etc/stunnel/certs/vpc.key sessionResume = no options = NO_TICKET retry=yes TIMEOUTclose = 0 debug=debug [in-iam] client=no accept = 172.18.3.2:443 connect=127.0.0.1:8082 cert = /etc/stunnel/certs/iam.pem key = /etc/stunnel/certs/iam.key sessionResume = no options = NO_TICKET retry=yes TIMEOUTclose = 0 debug=debug [out-hdt] client=yes accept=8080 connect=ip1:443 engineId=pkcs11 sni = hdt cert=pkcs11:model=ID%20Prime%20MD;manufacturer=Gemalto;serial=...;token=eToken;id=...;object=...;type=cert key=pkcs11:model=ID%20Prime%20MD;manufacturer=Gemalto;serial=...;token=eToken;id=...;object=...;type=private;pin-value=pin sessionResume = no options = NO_TICKET retry=yes TIMEOUTclose = 0 debug=debug [out-vpc] client=yes accept=8081 connect=ip2:443 engineId=pkcs11 sni = vpc cert=pkcs11:model=ID%20Prime%20MD;manufacturer=Gemalto;serial=...;token=eToken;id=...;object=...;type=cert key=pkcs11:model=ID%20Prime%20MD;manufacturer=Gemalto;serial=...;token=eToken;id=...;object=...;type=private;pin-value=pin sessionResume = no options = NO_TICKET retry=yes TIMEOUTclose = 0 debug=debug [out-iam] client=yes accept=8082 connect=ip3:443 engineId=pkcs11 sni = iam cert=pkcs11:model=ID%20Prime%20MD;manufacturer=Gemalto;serial=...;token=eToken;id=...;object=...;type=cert key=pkcs11:model=ID%20Prime%20MD;manufacturer=Gemalto;serial=...;token=eToken;id=...;object=...;type=private;pin-value=pin sessionResume = no options = NO_TICKET retry=yes TIMEOUTclose = 0 debug=debug When I try run in gdb: root@c6b200207f1a:/stunnel-5.76# gdb stunnel GNU gdb (Ubuntu 12.1-0ubuntu1~22.04.2) 12.1 Copyright (C) 2022 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html > This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <https://www.gnu.org/software/gdb/bugs/>. Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from stunnel... (gdb) r Starting program: /usr/local/bin/stunnel [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". [New Thread 0x7ffff789f640 (LWP 4875)] [Thread 0x7ffff789f640 (LWP 4875) exited] [New Thread 0x7ffff789f640 (LWP 4876)] [New Thread 0x7ffff6c78640 (LWP 4878)] free(): invalid pointer Thread 1 "stunnel" received signal SIGABRT, Aborted. __pthread_kill_implementation (no_tid=0, signo=6, threadid=140737346406208) at ./nptl/pthread_kill.c:44 44 ./nptl/pthread_kill.c: No such file or directory. (gdb) stunnel is running in docker container ubuntu:22.04 Can someone tell where is the problem? Regards BS

1 0

Was LOG3[per-minute]: OCSP: SSL_get_certificate for a shared secret, PSK, configuration fixed with 5.76?
by u34＠net9.cf 01 Nov '25

01 Nov '25

Hello, At [stunnel 5.76 released](https://www.stunnel.org/mailman3/hyperkitty/list/stunnel-users@st… - Missing OCSP stapling is no longer logged as an error. was mentioned in Bugfixes. My understanding is [LOG3[per-minute]: OCSP: SSL_get_certificate](https://www.stunnel.org/mailman3/hyperkitty/list/stunn… is fixed. But it isn't.

1 0

Should remote host IPs recorded at lower debug levels too?
by u34＠net9.cf 21 Oct '25

21 Oct '25

Does recording the IPs of the remote host depends on other configuration directives, other then the debug directive? Is it correct that at LOG5, IPs of the remote host are recorded at the log file? Is it correct that at LOG3, no IPs are recorded even when other information for a particular connection is considered worth recording? Aren't IPs considered important information worth recording when error conditions are recorded?

1 0

stunnel 5.76 released
by Michał Trojnara 18 Oct '25

18 Oct '25

Dear Users, I have released version 5.76 of stunnel. ### Version 5.76, 2025.10.18, urgency: MEDIUM * Security bugfixes - OpenSSL DLLs updated to version 3.5.4. - Service-level multivalued options now override (rather than append to) global defaults, preventing unintended configurations. * Bugfixes - Fixed enabling/disabling of the default fips=yes property. - Missing OCSP stapling is no longer logged as an error. - Fixed a crash when a PIN was required due to the PKCS#11 CKA_ALWAYS_AUTHENTICATE attribute. * Features - Quantum-resistant hybrid key agreement X25519+ML-KEM-768 (X25519MLKEM768) used by default with OpenSSL 3.5+ and TLS 1.3. - Multiple cert sources are supported, allowing a certificate to be fetched from a provider while loading the chain from a file. - Android build switched to a 16 KB page size. Home page: https://www.stunnel.org/ Download: https://www.stunnel.org/downloads.html SHA-256 hashes: cda37eb4d0fb1e129718ed27ad77b5735e899394ce040bb2be28bbb937fd79e1 stunnel-5.76.tar.gz d93c7c01366d38ebd27689d606e45197ba8e2e2a32d1a186a81d2b01186bfb56 stunnel-5.76-win64-installer.exe f081281c92f6dc245e23d57930f3963d0155a9fc4a707b7414c941e8e60a1957 stunnel-5.76-android.zip Best regards, Mike

1 0

LOG3[per-minute]: OCSP: SSL_get_certificate
by u34＠net9.cf 15 Oct '25

15 Oct '25

With stunnel version 5.74 and debug = 3 foreground = yes setgid = abcde setuid = abcde output = /path/to/log/file [service] PSKsecrets = /path/to/secretfile accept = ip1:port1 connect = ip2:port1 debug = 3 setgid = abcde setuid = abcde This configuration looks to me similar to the [shell] option from the configuration examples. There is a 1 per minute LOG3[per-minute]: OCSP: SSL_get_certificate line at the log file. Does it a bug? This wasn't discussed 3 weeks ago at [How to get rid of "No OCSP stapling response received" warning?](https://www.stunnel.org/mailman3/hyperkitty/list/stunnel-users@st…, was it?

1 0

Client mode certificate pinning
by Ian Pilcher 11 Oct '25

11 Oct '25

Is $SUBJECT possible? I use stunnel to connect to my old "smart" switches that don't support modern TLS protocols, ciphers, etc. Recently, their existing certificates all expired, and I tried to install new certificates on all of them, only to discover that they won't accept my new CA certificate, because it was signed with a 3072-bit key. I could go through the trouble of generating a separate CA certificate with a 2048-bit key, sign new certificates with that key, etc., etc., but it starts to seem a bit silly at that point. Far better to simply generate a self-signed certificate for each switch and configure stunnel to only accept that particular certificate (i.e. "pin" it). Is this possible with stunnel? If so, how would I go about configuring it to do this? (Search engines are telling me to use "verify = 4", but stunnel(8) says that option is obsolete.) TIA! -- ======================================================================== If your user interface is intuitive in retrospect ... it isn't intuitive ========================================================================

2 1

How to get rid of "No OCSP stapling response received" warning?
by Ian Pilcher 25 Sep '25

25 Sep '25

I use stunnel to connect to my old "smart" switches from modern browsers. Here is a subset of the configuration for one of the switches. [switch1-frontend] sni = frontend:switch1.penurio.us CAfile = /etc/ipa/ca.crt cert = /etc/pki/tls/certs/stunnel/switch1.crt key = /tmp/keys/switch1.key connect = 127.255.255.254:8081 [switch1-backend] client = yes accept = 127.255.255.254:8081 connect = 172.31.4.1:443 verifyChain = yes checkHost = switch1.penurio.us CAfile = /etc/ipa/ca.crt sslVersion = TLSv1 ciphers = DHE-RSA-AES256-SHA options = ALLOW_UNSAFE_LEGACY_RENEGOTIATION securityLevel = 0 OCSPrequire = no OCSPaia = no Everything works, execept that every connection produces a bright red warning in my log: OCSP: No OCSP stapling response received I've read up on OCSP stapling, that this seems to mean that the switch isn't including an OCSP response in its TLS handshake. (Hardly surprising, given its age.) How can I tell stunnel to not request/expect an OCSP response from the switch (or at least to not log the missing OCSP response as a warning)? -- ======================================================================== If your user interface is intuitive in retrospect ... it isn't intuitive ========================================================================

4 5

stunnel FIPS mode 140-2/ Other Modes
by mehmet ozisik 19 Sep '25

19 Sep '25

Hi All, I would like to ask a question about stunnel fips mode. There are lots of question and answers on the internet related with this, but I could not find any answer related with mine. I am compiling with openssl (auto detecting fips) . Here is a part of confgiure output : checking for FIPS_mode_set... yes configure: FIPS mode detected So I am thinking that fips also is being included. Then I try to run stunnel on target platform (in stunnel.conf fips=yes) and it gives below error : Compiled/running with OpenSSL 0.9.8w-fips 23 Apr 2012 Threading:PTHREAD Sockets:POLL,IPv6 SSL:ENGINE,OCSP,FIPS Reading configuration from file stunnel.conf FIPS_mode_set: 2D06906E: error:2D06906E:FIPS routines:FIPS_CHECK_INCORE_FINGERPRINT:fingerprint does not match there are lots of information about this errror on internet. Then when I configure stunnel.conf with fips=no, stunnel is running successfully. I know that fips=yes means that enables FIPS 140-2 mode and I guess my fips canister does not supoort fips 140-2 mode (I do not know which fips mode it has supported). Now my question is coming : When I set fips=no, stunnel also starts with other available fips modes which the canister included? Or it skips running fips mode completely? Plase inform me if anyone has any idea? Regards

2 1

Stunnel, Gmail and Outlook Express
by landjonline＠hotmail.com 01 Sep '25

01 Sep '25

I have Outlook Express and my email addresses are Gmail. Is there a way to get Gmail to work with Outlook Express using Stunnel? Thanks

2 1

Using CAStore on Android (stunnel.conf)
by smf.forum1＠ntlworld.com 31 Jul '25

31 Jul '25

I have build stunnel with a few changes to run in a QThread (Qt 6.9.1) for Android. My Qt App starts stunnel at the start of execution and stops it when my Qt application exits. This all works fine (I need to review and clean up my stunnel changes before I use my solution for real) but I cannot get certification to work, here are two test runs one with verify set to 0 (works) and verify set to 2 (fails). What needs to change in my stunnel.conf file ? Thanks. (obfuscated details) stunnel.conf foreground = yes debug = 6 [mariadb] CAstore = /data/misc/user/0/cacerts-added CApath = /data/misc/user/0/cacerts-added client = yes accept = 127.0.0.1:3307 connect = remote_server:3307 verify = 0 Works: I/stunnel : LOG6[ui]: Initializing inetd mode configuration I/stunnel : LOG5[ui]: stunnel 5.75 on android-mobile-device platform I/stunnel : LOG5[ui]: Compiled/running with OpenSSL 3.1.1 30 May 2023 I/stunnel : LOG5[ui]: Threading:PTHREAD Sockets:SELECT,IPv4 TLS:ENGINE,OCSP,PSK,SNI I/stunnel : LOG6[ui]: Initializing inetd mode configuration I/stunnel : LOG5[ui]: Reading configuration from buffer 0x7280e409b640 I/stunnel : LOG5[ui]: UTF-8 byte order mark not detected I/stunnel : LOG6[ui]: Compression disabled I/stunnel : LOG6[ui]: Initializing service [mariadb] I/stunnel : LOG6[ui]: stunnel default security level set: 2 I/stunnel : LOG6[ui]: Session resumption enabled I/stunnel : LOG6[ui]: Configured trusted server CA: C=AU, ST=Florida, L=York, O=Home, OU=Whiskey, CN=Michael, emailAddress=eric.admin(a)intheether.com W/stunnel : LOG4[ui]: Service [mariadb] needs authentication to prevent MITM attacks I/stunnel : LOG6[ui]: DH initialization skipped: client section I/stunnel : LOG5[ui]: Configuration successful I/stunnel : LOG6[ui]: Service [mariadb] (FD=117) bound to 127.0.0.1:3307 I/stunnel : LOG6[ui]: Accepting new connections I/stunnel : LOG6[per-day]: Executing per-day jobs I/stunnel : LOG6[per-day]: Per-day jobs completed in 0 seconds I/stunnel : LOG5[0]: Service [mariadb] accepted connection from 127.0.0.1:36802 I/stunnel : LOG6[0]: s_connect: connecting 192.168.0.1:3307 I/stunnel : LOG5[0]: s_connect: connected 192.168.0.1:3307 I/stunnel : LOG5[0]: Service [mariadb] connected remote server from 10.0.2.16:58660 I/stunnel : LOG6[0]: SNI: sending servername: remote_server I/stunnel : LOG6[0]: Peer certificate not required I/stunnel : LOG6[0]: Received trusted client CA: C=AU, ST=Florida, L=York, O=Home, OU=Whiskey, CN=Michael, emailAddress=eric.admin(a)intheether.com I/stunnel : LOG6[0]: CERT: Certificate verification disabled I/stunnel : LOG6[0]: CERT: Certificate verification disabled I/stunnel : LOG6[0]: OCSP: Certificate chain verification disabled I/stunnel : LOG6[0]: TLS connected: new session negotiated I/stunnel : LOG6[0]: TLSv1.3 ciphersuite: TLS_AES_256_GCM_SHA384 (256-bit encryption) I/stunnel : LOG6[0]: Peer temporary key: X25519, 253 bits I/stunnel : LOG6[0]: Session id: 90DD6325CCBC47C3F8F560C36F76755B4959E6A8421DD97B751E37FDD1DCCAC7 I/stunnel : LOG6[0]: Session id: 24345E21753FE3B254CA089FB7621C1481B523E72EB9571DDF7A366B5E89E834 stunnel.conf foreground = yes debug = 6 [mariadb] CAstore = /data/misc/user/0/cacerts-added CApath = /data/misc/user/0/cacerts-added client = yes accept = 127.0.0.1:3307 connect = remote_server:3307 verify = 2 Fails: I/stunnel : LOG6[ui]: Initializing inetd mode configuration I/stunnel : LOG5[ui]: stunnel 5.75 on android-mobile-device platform I/stunnel : LOG5[ui]: Compiled/running with OpenSSL 3.1.1 30 May 2023 I/stunnel : LOG5[ui]: Threading:PTHREAD Sockets:SELECT,IPv4 TLS:ENGINE,OCSP,PSK,SNI I/stunnel : LOG6[ui]: Initializing inetd mode configuration I/stunnel : LOG5[ui]: Reading configuration from buffer 0x7280e409b0a0 I/stunnel : LOG5[ui]: UTF-8 byte order mark not detected I/stunnel : LOG6[ui]: Compression disabled I/stunnel : LOG6[ui]: Initializing service [mariadb] I/stunnel : LOG6[ui]: stunnel default security level set: 2 I/stunnel : LOG6[ui]: Session resumption enabled I/stunnel : LOG6[ui]: Configured trusted server CA: C=AU, ST=Florida, L=York, O=Home, OU=Whiskey, CN=Michael, emailAddress=eric.admin(a)intheether.com W/stunnel : LOG4[ui]: Service [mariadb] uses "verifyChain" without subject checks W/stunnel : LOG4[ui]: Use "checkHost" or "checkIP" to restrict trusted certificates I/stunnel : LOG6[ui]: DH initialization skipped: client section I/stunnel : LOG5[ui]: Configuration successful I/stunnel : LOG6[ui]: Service [mariadb] (FD=114) bound to 127.0.0.1:3307 I/stunnel : LOG6[ui]: Accepting new connections I/stunnel : LOG6[per-day]: Executing per-day jobs I/stunnel : LOG6[per-day]: Per-day jobs completed in 0 seconds I/stunnel : LOG5[0]: Service [mariadb] accepted connection from 127.0.0.1:39238 I/stunnel : LOG6[0]: s_connect: connecting 192.168.0.1:3307 I/stunnel : LOG5[0]: s_connect: connected 192.168.0.1:3307 I/stunnel : LOG5[0]: Service [mariadb] connected remote server from 10.0.2.16:59154 I/stunnel : LOG6[0]: SNI: sending servername: remote_server I/stunnel : LOG6[0]: Peer certificate required I/stunnel : LOG6[0]: Received trusted client CA: C=AU, ST=Florida, L=York, O=Home, OU=Whiskey, CN=Michael, emailAddress=eric.admin(a)intheether.com W/stunnel : LOG4[0]: CERT: Pre-verification error: certificate not found in local repository: self-signed certificate W/stunnel : LOG4[0]: Rejected by CERT at depth=0: C=PL, ST=Mazovia Province, L=Warsaw, O=Stunnel Developers, OU=Provisional CA, CN=localhost E/stunnel : LOG3[0]: SSL_connect: tls_post_process_server_certificate@ssl/statem/statem_clnt.c:1890: error:0A000086:SSL routines::certificate verify failed I/stunnel : LOG5[0]: Connection closed/reset: 0 byte(s) sent to TLS, 0 byte(s) sent to socket I/stunnel : LOG6[ui]: Child process 17669 finished with code 0

1 0

Android Stunnel 64bit version
by emxacademy＠gmail.com 18 Jul '25

18 Jul '25

Hello everyone, I've been searching online but still haven’t found a clear or working method to build a 64-bit version of the Android stunnel executable. Since most Android devices now run on 64-bit architecture, the 32-bit version available on the official website no longer works on many phones. If anyone has experience with this or can guide me through the proper way to compile a 64-bit version, I’d really appreciate your help. Thanks in advance!

1 0

Error message when trying to set Stunnel as a start up app
by Edward Smithson 18 Jul '25

18 Jul '25

Hello Stunnel mailing list, We are trying to set Stunnel (5.75) to automatically open as a start up app on Windows 11. When the PC powers up, it gives this error message: stunnel.exe - System Error The code execution cannot proceed because libcrypto-3-x64.dll was not found. Reinstalling the program may fix this problem. We have tried reinstalling, but to no avail. NB, Stunnel works fine if opened manually. This was not an issue with Windows 10. Has anyone else had this problem (and solved it)? Many thanks, Ed Smithson Ed Smithson Reader Services Librarian Nuffield College, Oxford, OX1 1NF +44(0) 1865 278551 [cid:[email protected]]<https://bsky.app/profile/nuffieldlibrary.bsky.social>[cid:[email protected]]<https://www.facebook.com/NuffieldCollegeLibrary>[cid:[email protected]]<https://www.instagram.com/nuffieldlibrary/> [cid:[email protected]]<https://www.nuffield.ox.ac.uk/>

5 6

stunnel with aurora postgreSQL
by Grube, Rolf | Oberender AG 25 Jun '25

25 Jun '25

Hi everybody, Does anybody has already established a connection to AWS aurora postgreSQL with stunnel? I cant establish a connection and it may be an issue with channel binding. My config looks like this: ; Sample stunnel configuration file for Win64 by Michal Trojnara 1998-2025 ; Some options used here may be inadequate for your particular configuration ; This sample file does *not* represent stunnel.conf defaults ; Please consult the manual for detailed description of available options ; ************************************************************************** ; * Global options * ; ************************************************************************** ; Debugging stuff (may be useful for troubleshooting) debug = 7 output = stunnel.log ; Enable FIPS 140-2 mode if needed for compliance fips = yes ; The CNG engine allows to integrate stunnel with the Windows Cryptography API: ; Next Generation (CNG) for authentication with private keys stored in the ; Windows certificate store. It serves as a drop-in replacement for the legacy ; OpenSSL Cryptography API (CAPI) engine. ; https://www.stunnel.org/cng-engine.html ; Each section using this feature also needs the "engineId = cng" option engine = cng ; The pkcs11 engine allows for authentication with cryptographic ; keys isolated in a hardware or software token ; MODULE_PATH specifies the path to the pkcs11 module shared library, ; such as softhsm2-x64.dll or opensc-pkcs11.dll ; IMPORTANT: A 64-bit stunnel requires 64-bit PKCS#11 modules ; Each section using this feature also needs the "engineId = pkcs11" option ;engine = pkcs11 ;engineCtrl = MODULE_PATH:softhsm2-x64.dll ;engineCtrl = PIN:1234 ; ************************************************************************** ; * Service defaults may also be specified in individual service sections * ; ************************************************************************** ; Enable support for the insecure SSLv3 protocol ;options = -NO_SSLv3 ; These options provide additional security at some performance degradation ;options = SINGLE_ECDH_USE ;options = SINGLE_DH_USE ; ************************************************************************** ; * Include all configuration file fragments from the specified folder * ; ************************************************************************** ;include = conf.d ; ************************************************************************** ; * Service definitions (at least one service has to be defined) * ; ************************************************************************** [postgreSQL_TLS] client = yes ;engineId = cng accept = 5433 connect = xxx.rds.amazonaws.com:5432 protocol = pgsql CAfile = C:\cert\xxx-bundle.pem verifyChain = yes checkHost = xxx.rds.amazonaws.com Thanks for any recommendations. Best regards Rolf Grube, MBA Senior Manager <https://www.credly.com/badges/443267d6-0d25-4fc3-9eee-f9654f6f3ee1/public_u rl> Oberender AG Elsenheimerstraße 59 | 80687 München t: +49 89 8207516-0 | m: +49 173 2035 133 <mailto:[email protected]> rolf.grube(a)oberender.com <http://www.oberender.com/> www.oberender.com Vorsitzender des Aufsichtsrats: Dipl.-Volkswirtin Irmtraut Gürkan Vorstand: Jan Hacker (Vorsitzender), Jochen Baierlein Handelsregister: Amtsgericht Bayreuth, HRB 4267 Sitz der Gesellschaft: Bayreuth Diese E-Mail enthält vertrauliche und/oder rechtlich geschützte Informationen. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese Mail. Das unerlaubte Kopieren, sowie die unbefugte Weitergabe dieser Mail sind nicht gestattet.

1 0

Duplicate Received trusted client CA messages
by Sean Burford 18 Jun '25

18 Jun '25

Hi, While configuring stunnel to connect as a client to a TLS server that requires client certificate auth (known as mutual TLS auth), I noticed that each new connection generates lots (up to hundreds) of duplicate logs like: 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA I expect one log per trusted client CA provided by the server. Openssl s_client -msg shows that the server only sends a small CertificateRequest. Stunnel logs show that only one connection is made. This only happens if the server offers exactly one trusted client CA. If multiple client CA options are offered by the server then a single log entry is recorded for each. What appears to be happening is that OpenSSL’s state machine generates lots of info callbacks (the number depends on latency). This appears to be harmless except for the excessive logging. I’m running stunnel 5.75 against OpenSSL 3.5.0 (compiled with enable-weak-ssl-ciphers, enable-ssl3 and enable-ssl3-method): $ stunnel [ ] Initializing inetd mode configuration [ ] Clients allowed=125 [.] stunnel 5.75 on sparc-sun-solaris2.10 platform [.] Compiled/running with OpenSSL 3.5.0 8 Apr 2025 [.] Threading:PTHREAD Sockets:POLL,IPv6 TLS:ENGINE,OCSP,PSK,SNI [ ] errno: (*(___errno())) … $ openssl version OpenSSL 3.5.0 8 Apr 2025 (Library: OpenSSL 3.5.0 8 Apr 2025) This is probably NOT caused by an OpenSSL 3.5.0 behaviour change, I also see duplicate messages from the public stunnel build running on Windows: [ ] Initializing inetd mode configuration [ ] Running on Windows 6.2 [ ] No limit detected for the number of clients [.] stunnel 5.74 on x64-pc-mingw32-gnu platform [.] Compiled/running with OpenSSL 3.3.2 3 Sep 2024 [.] Threading:WIN32 Sockets:SELECT,IPv6 TLS:ENGINE,FIPS,OCSP,PSK,SNI [ ] errno: (*_errno()) To diagnose this further, I modified stunnel src/ctx.c info_callback() to log the TLS state in callbacks: //#if 0 // s_log(LOG_DEBUG, "state = %x", state); state_string=SSL_state_string_long(ssl); s_log(LOG_DEBUG, "TLS state (where %08X state %08X): %s", where, state, state_string); //#endif This shows that there are many callbacks from where SSL_CB_ACCEPT_EXIT and one final callback from SSL_CB_ACCEPT_LOOP: 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA 2025.06.18 10:23:58 LOG7[0]: TLS state (where 00001002 state 00000008): SSLv3/TLS read server certificate request 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA 2025.06.18 10:23:58 LOG7[0]: TLS state (where 00001002 state 00000008): SSLv3/TLS read server certificate request 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA 2025.06.18 10:23:58 LOG7[0]: TLS state (where 00001002 state 00000008): SSLv3/TLS read server certificate request 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA 2025.06.18 10:23:58 LOG7[0]: TLS state (where 00001001 state 00000008): SSLv3/TLS read server certificate request 2025.06.18 10:23:58 LOG6[0]: Received trusted client CA: CN=Example CA 2025.06.18 10:23:58 LOG7[0]: TLS state (connect): SSLv3/TLS read server certificate request Modifying info_callback to look for SSL_CB_LOOP in where suppresses the excess messages: /* log the client certificate request (if received) */ #ifndef SSL3_ST_CR_CERT_REQ_A if(state==TLS_ST_CR_CERT_REQ && *where & SSL_CB_LOOP*) #else if(state==SSL3_ST_CR_CERT_REQ_A && *where & SSL_CB_LOOP*) #endif print_CA_list("Received trusted client CA", SSL_get_client_CA_list(ssl)); Here’s my config: debug=info [outbound-http-to-https-mtls] accept = 127.0.0.1:8447 connect = 127.0.0.1:8445 client = yes ; verify 2 - verify peer certificate chain verify = 2 sni = www.example.com checkHost = www.example.com verifyChain = yes CAfile = /export/home/user/stunnel/trusted-ca-certs.pem ; Authenticate ourselves to peer using a client certificate. cert = /export/home/user/stunnel/user.ecdsa-p256.pem key = /export/home/user/stunnel/user.ecdsa-p256.key -- Thanks, Sean Burford

1 0

[PATCH 0/3] Improve stunnel performance by ~17%
by Edwin Torok 12 Jun '25

12 Jun '25

Hello, Flamegraph profiling on stunnel has shown that most time is NOT spent in encryption/decryption, but in sending/receiving data. Experimental setup: ``` CPU: 2x 18-core Intel Xeon Gold 6354 NIC: Intel E810-XXV, 100 Gbit/s Kernel: 6.14.8-300.fc42.x86_64 x86_64 Mem: 251.32 GiB OS: Fedora Linux 42 openssl version: OpenSSL 3.2.4 11 Feb 2025 (Library: OpenSSL 3.2.4 11 Feb 2025) stunnel: 5.75 from git ``` Network, encryption and memory copy speeds converted into Gbit/s on the above HW: ``` iperf3: 40Gbit/s openssl speed -evp aes-256-gcm: 72Gbit/s perf bench memcpy: 100Gbit/s ``` Under ideal conditions we should be able to achieve at most ~20.5Gbit/s, however I only measured ~7.6Gbit/s. The scripts that I used to perform measurements are included in the attached patch 3. See also related discussion on curl: https://github.com/curl/curl/pull/17548 Enabling readahead, avoiding excessive alloc/free of buffers, increasing buffer sizes, and improving buffer handling can all improve performance. For now I'm sending just the first small patches as proofs of concept, each of them one-liners. I hope you can include these in some form in the next release. Eventually these should probably be exposed as configuration flags in stunnel.conf, I can help implementing that, or I can leave implementing that to you if you prefer. In fact readahead was enabled in previous versions of stunnel, and then disabled again, so I assume you ran into some bugs with it on certain protocols? Increasing the buffer size is not a clear win (as with curl), due to the excessive use of memmove/memset, and that SSL_read/SSL_write only still processes 1 TLS record at a time. I have some further changes that can improve that, but the patches are larger and I haven't finished testing them for correctness yet. Please let me know if you'd want these as patches, or if you'd rather implement them yourself. Edwin Török (3): openssl: enable readahead openssl: disable SSL_MODE_RELEASE_BUFFERS Benchmark scripts src/ctx.c | 5 +- tests/benchmark/benchmark.sh | 120 +++++++++++++++++++++++ tests/benchmark/launch.sh | 185 +++++++++++++++++++++++++++++++++++ 3 files changed, 309 insertions(+), 1 deletion(-) create mode 100644 tests/benchmark/benchmark.sh create mode 100755 tests/benchmark/launch.sh -- 2.43.5

4 6

Is TLS 1.2 supported with stunnel 5.01
by joverton＠vital-soft.com 01 Jun '25

01 Jun '25

I have searched online, but was unable to fine any definitive answer on the minimum version of stunnel required for TLS 1.2. I have a client using stunnel 5.01 with our solution and they want to activate TLS 1.2. Their setup looks like this: 2014.05.15 13:38:22 LOG5[10132]: stunnel 5.01 on x86-pc-msvc-1500 platform 2014.05.15 13:38:22 LOG5[10132]: Compiled/running with OpenSSL 1.0.1g-fips 7 Apr 2014 2014.05.15 13:38:22 LOG5[10132]: Threading:WIN32 Sockets:SELECT,IPv6 SSL:ENGINE,OCSP,FIPS 2014.05.15 13:38:22 LOG5[10132]: Reading configuration from file stunnel.conf 2014.05.15 13:38:22 LOG5[10132]: FIPS mode disabled 2014.05.15 13:38:22 LOG5[10132]: Configuration successful Everything works fine without requiring TLS 1.2, but when that is required, we get the following error: 2025.05.14 07:04:45 LOG7[3796]: SSL state (connect): before/connect initialization 2025.05.14 07:04:45 LOG7[3796]: SSL state (connect): SSLv3 write client hello A 2025.05.14 07:04:45 LOG7[3796]: SSL alert (read): fatal: protocol version 2025.05.14 07:04:45 LOG3[3796]: SSL_connect: 1409442E: error:1409442E:SSL routines:SSL3_READ_BYTES:tlsv1 alert protocol version 2025.05.14 07:04:45 LOG5[3796]: Connection reset: 0 byte(s) sent to SSL, 0 byte(s) sent to socket 2025.05.14 07:04:45 LOG7[3796]: Remote socket (FD=840) closed 2025.05.14 07:04:45 LOG7[3796]: Local socket (FD=832) closed - Do we need to change anything in stunnel.conf? - Do we need to upgrade stunnel? Many Thanks, John

4 5

Re: stunnel 5.75 released
by Christian Ullrich 28 May '25

28 May '25

* Michal Trojnara wrote: > I have released version 5.75 of stunnel. > > ### Version 5.75, 2025.05.26, urgency: MEDIUM Hello, why does the Windows release include "libgcc_s_seh-1.dll"? I cannot find anything that uses it, and a basic configuration works without any attempts to load it. I went to some lengths to find indications it might be loaded dynamically, but found nothing. Thanks, -- Christian

2 1

stunnel 5.75 released
by Michał Trojnara 26 May '25

26 May '25

Dear Users, I have released version 5.75 of stunnel. ### Version 5.75, 2025.05.26, urgency: MEDIUM * Security bugfixes - OpenSSL DLLs updated to version 3.4.1. - OpenSSL FIPS Provider updated to version 3.1.2. * Bugfixes - Fixed infinite loop triggered by OCSP URL parsing errors (thx to Richard Könning for reporting). - Fixed OPENSSL_NO_OCSP build issues (thx to Dmitry Mostovoy for reporting). - Fixed default curve selection in FIPS mode with OpenSSL 3.4+. - Fixed tests with modern Python versions. - Fixed tests with multiple OpenSSL versions installed. * Features - Added provider URI support for "cert" and "key" options. - Added new "CAstore" service-level option (OpenSSL 3.0+). - Added "provider" (OpenSSL 3.0+), "providerParameter" (OpenSSL 3.5+), and "setEnv" global options. - Key file/URI path added to passphrase prompt on Unix. - PKCS#11 provider installed on Windows. Home page: https://www.stunnel.org/ Download: https://www.stunnel.org/downloads.html SHA-256 hashes: 0c1ef0ed85240974dccb94fe74fb92d6383474c7c0d10e8796d1f781a3ba5683 stunnel-5.75.tar.gz 18ec3b83bda9143c79479ecdc1e3ecf515eeb8a8b11e6ea3a6856cd77399317d stunnel-5.75-win64-installer.exe d1a04ec51840d8cbf5fb6d897d2eb999af573b5b66268fdec109cddaff2acfb7 stunnel-5.75-android.zip Best regards, Mike

1 0

Preserving Client IP Address
by atritium＠hushmail.com 21 May '25

21 May '25

Has anyone followed the stunnel man page instructions and been able to successfully pass/preserve the connecting client's original IP address? Checking history on this issue back to 2010, it looks people with problems, no reports of success. Though it seems so fundamental, you would hope it was smooth as the man page indicates For example, I set up an iptables 'mangle' table for DIVERT routing, ip rule, ip route, etc, for the server as given in the stunnel man page for a Red Hat 8 system. When the stunnel server is then also configured with "transparent = source" and restarted, the remote-initiated connection -hangs- without connecting for a few seconds before closing. Take out "transparent = source" from the server config, and the connection works successfully (though the client IP address is not available to applications). Logs are the same up until the point (shown below), which shows the "hanging/failed" case timing out after reporting "Cannot assign an AF=2 address an AF=10 socket". Don't know what the "Cannot assign AF ..." refers to, or how to address it, but the process goes downhill and hangs after that. 7111 is the open port stunnel is monitoring. 2025.05.21 10:07:16 LOG7[0]: Cannot assign an AF=2 address an AF=10 socket 2025.05.21 10:07:16 LOG6[0]: IP_TRANSPARENT socket option set 2025.05.21 10:07:16 LOG6[0]: bind succeeded on the original port 2025.05.21 10:07:16 LOG6[0]: s_connect: connecting 127.0.0.1:7111 2025.05.21 10:07:16 LOG7[0]: s_connect: s_poll_wait 127.0.0.1:7111: waiting 10 seconds 2025.05.21 10:07:16 LOG7[0]: FD=6 events=0x2001 revents=0x0 2025.05.21 10:07:16 LOG7[0]: FD=11 events=0x2005 revents=0x1 2025.05.21 10:07:26 LOG3[0]: s_connect: s_poll_wait 127.0.0.1:7111: TIMEOUTconnect exceeded 2025.05.21 10:07:26 LOG3[0]: No more addresses to connect 2025.05.21 10:07:26 LOG5[0]: Connection reset: 0 byte(s) sent to TLS, 0 byte(s) sent to socket 2025.05.21 10:07:26 LOG7[0]: local_rfd/local_wfd reset (FD=3) 2025.05.21 10:07:26 LOG7[0]: Local descriptor (FD=3) closed 2025.05.21 10:07:26 LOG7[0]: Service [TLS SERVER] finished (0 left) The log for the successful case when "transparent = source is NOT specified in server config) instead says: 2025.05.21 09:59:58 LOG6[0]: s_connect: connecting ::1:7111 2025.05.21 09:59:58 LOG7[0]: s_connect: s_poll_wait ::1:7111: waiting 10 seconds 2025.05.21 09:59:58 LOG7[0]: FD=6 events=0x2001 revents=0x0 2025.05.21 09:59:58 LOG7[0]: FD=11 events=0x2005 revents=0x1 2025.05.21 09:59:58 LOG5[0]: s_connect: connected ::1:7111 2025.05.21 09:59:58 LOG6[0]: persistence: ::1:7111 cached 2025.05.21 09:59:58 LOG5[0]: Service [TLS SERVER] connected remote server from ::1:49806 2025.05.21 09:59:58 LOG7[0]: Setting remote socket options (FD=11) Any insight on what "Cannot assign an AF=2 address an AF=10 socket" is and how to fix it to preserve client IP address? stunnel is running as root, setuid is not used. I might not correctly understand the man page comment "This option is currently available in: Remote mode (connect option) on Linux >=2.6.28", but think it means a normal external connection request. Hopefully not a special configuration on the client side.

1 0

SSL_CTX_load_verify_locations: Peer suddenly disconnected
by lynn9a＠yahoo.com 13 May '25

13 May '25

Hi, All When we try to start stunnel(stunnel 5.67, wolfSSL5.6.4 on linux), there is an error randomly happened like following, anybody knows why this happen and how to fix this? Thanks May 9 09:09:01 [ ] Initializing inetd mode configuration May 9 09:09:01 [ ] Clients allowed=500 May 9 09:09:01 [.] stunnel 5.67 on arm-oe-linux-gnueabi platform May 9 09:09:01 [.] Compiled/running with wolfSSL 5.6.4 May 9 09:09:01 [.] Threading:PTHREAD Sockets:POLL,IPv6,SYSTEMD TLS:OCSP,PSK,SNI May 9 09:09:01 [ ] errno: (*__errno_location ()) May 9 09:09:01 [ ] Initializing inetd mode configuration May 9 09:09:01 [.] Reading configuration from file /opt/config/stunnel.conf May 9 09:09:01 [.] UTF-8 byte order mark not detected May 9 09:09:01 [ ] No PRNG seeding was required May 9 09:09:01 [ ] Initializing service [xxxHost] May 9 09:09:01 [ ] stunnel default security level set: 2 May 9 09:09:01 [ ] Ciphers: TLS_AES_256_GCM_SHA384 May 9 09:09:01 [ ] TLSv1.3 ciphersuites: TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_CHACHA20_POLY1305_SHA256 May 9 09:09:01 [ ] TLS options: 0x4D474C4C003000 (+0x0, -0x0) May 9 09:09:01 [ ] Session resumption enabled May 9 09:09:01 [ ] Loading certificate from file: ./config/client.pem May 9 09:09:01 [ ] Certificate loaded from file: ./config/client.pem May 9 09:09:01 [ ] Loading private key from file: ./config/client.key May 9 09:09:01 [:] Insecure file permissions on ./config/client.key May 9 09:09:01 [ ] Private key loaded from file: ./config/client.key May 9 09:09:01 [ ] Private key check succeeded May 9 09:09:01 [!] SSL_CTX_load_verify_locations: Peer suddenly disconnected May 9 09:09:01 [!] Service [xxxHost]: Failed to initialize TLS context May 9 09:09:01 [!] Configuration failed May 9 09:09:01 [ ] Deallocating temporary section defaults May 9 09:09:01 [ ] Deallocating section [xxxHost]

3 2

Using intermediate CA as a trust anchor in stunnel
by Vít Holásek 30 Mar '25

30 Mar '25

Hi, I'm trying to setup stunnel to trust only certificates issued by intermediate CA and not other CAs issues by the same root CA. I came across this discussion about the same topic: https://www.stunnel.org/ mailman3/hyperkitty/list/stunnel-users(a)stunnel.org/thread/DUF6C6 BRNFVAWVCDIGXPUDTAPZR5KV5W/. I tested described options but it always authenticates also other sub CAs, because the whole chain must be always supplied in configured CAfile or CApath. In my opinion, the proper solution would be to add "partial chain" OpenSSL configuration option to stunnel config. This would allow admin to decide how intermediate CA will be verified. What do you think about that? See corresponding OpenSSL issue: https://github.com/openssl/openssl/issues/ 7871. Thanks Vit

1 0

stunnel - client conexion close by TLS alert (write) fatal decode error
by Rodigo Alvarez 07 Mar '25

07 Mar '25

Hi All! I would appreciate any clue to solve the problem we are having with a client mode service that stopped working this week (we verified that the service works directly without stunnel). The error I identify in the trace is the following: "TLS alert (write): fatal: decode error" Stunnel Config (windows version): [afip-prod-fce] client = yes accept = ARSASSRV4DMS06:1031 connect = serviciosjava.afip.gob.ar:443 debug = 7 ws: https://serviciosjava.afip.gob.ar/wsfecred/FECredService Complete trace: 2024.01.24 09:28:46 LOG5[main]: stunnel 5.71 on x64-pc-mingw32-gnu platform 2024.01.24 09:28:46 LOG5[main]: Compiled/running with OpenSSL 3.1.3 19 Sep 2023 2024.01.24 09:28:46 LOG5[main]: Threading:WIN32 Sockets:SELECT,IPv6 TLS:ENGINE,OCSP,PSK,SNI 2024.01.24 09:28:46 LOG5[main]: Reading configuration from file C:\Program Files (x86)\stunnel\config\stunnel.conf 2024.01.24 09:28:46 LOG5[main]: UTF-8 byte order mark detected 2024.01.24 09:28:46 LOG5[main]: FIPS mode disabled 2024.01.24 09:28:46 LOG4[main]: Service [afip-prod-fce] needs authentication to prevent MITM attacks 2024.01.24 09:28:46 LOG5[main]: Configuration successful 2024.01.24 09:29:23 LOG7[0]: Service [afip-prod-fce] started 2024.01.24 09:29:23 LOG7[0]: Setting local socket options (FD=892) 2024.01.24 09:29:23 LOG7[0]: Option TCP_NODELAY set on local socket 2024.01.24 09:29:23 LOG5[0]: Service [afip-prod-fce] accepted connection from 10.70.162.24:57723 2024.01.24 09:29:23 LOG6[0]: s_connect: connecting 200.1.116.19:443 2024.01.24 09:29:23 LOG7[0]: s_connect: s_poll_wait 200.1.116.19:443: waiting 10 seconds 2024.01.24 09:29:23 LOG7[0]: FD=896 ifds=rwx ofds=--- 2024.01.24 09:29:24 LOG5[0]: s_connect: connected 200.1.116.19:443 2024.01.24 09:29:24 LOG5[0]: Service [afip-prod-fce] connected remote server from 10.72.0.69:64788 2024.01.24 09:29:24 LOG7[0]: Setting remote socket options (FD=896) 2024.01.24 09:29:24 LOG7[0]: Option TCP_NODELAY set on remote socket 2024.01.24 09:29:24 LOG7[0]: Remote descriptor (FD=896) initialized 2024.01.24 09:29:24 LOG6[0]: SNI: sending servername: serviciosjava.afip.gob.ar 2024.01.24 09:29:24 LOG6[0]: Peer certificate not required 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): before SSL initialization 2024.01.24 09:29:24 LOG7[0]: Initializing application specific data for session authenticated 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS write client hello 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS write client hello 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS read server hello 2024.01.24 09:29:24 LOG6[0]: CERT: Certificate verification disabled 2024.01.24 09:29:24 LOG6[0]: CERT: Certificate verification disabled 2024.01.24 09:29:24 LOG6[0]: CERT: Certificate verification disabled 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS read server certificate 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS read server key exchange 2024.01.24 09:29:24 LOG7[0]: OCSP stapling: Client callback called 2024.01.24 09:29:24 LOG6[0]: OCSP: Certificate chain verification disabled 2024.01.24 09:29:24 LOG6[0]: Client certificate not requested 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS read server done 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS write client key exchange 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS write change cipher spec 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS write finished 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS write finished 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS read change cipher spec 2024.01.24 09:29:24 LOG7[0]: TLS state (connect): SSLv3/TLS read finished 2024.01.24 09:29:24 LOG7[0]: New session callback 2024.01.24 09:29:24 LOG7[0]: Peer certificate was cached (6643 bytes) 2024.01.24 09:29:24 LOG6[0]: Session id: D63C79766AC02C9A3E8494AD528954A183E9F7C250856695BA05C16A2219A4B3 2024.01.24 09:29:24 LOG7[0]: 1 client connect(s) requested 2024.01.24 09:29:24 LOG7[0]: 1 client connect(s) succeeded 2024.01.24 09:29:24 LOG7[0]: 0 client renegotiation(s) requested 2024.01.24 09:29:24 LOG7[0]: 0 session reuse(s) 2024.01.24 09:29:24 LOG6[0]: TLS connected: new session negotiated 2024.01.24 09:29:24 LOG6[0]: TLSv1.2 ciphersuite: ECDHE-RSA-AES128-GCM-SHA256 (128-bit encryption) 2024.01.24 09:29:24 LOG6[0]: Peer temporary key: ECDH, P-256, 256 bits 2024.01.24 09:29:24 LOG7[0]: Compression: null, expansion: null 2024.01.24 09:29:24 LOG7[0]: Remove session callback 2024.01.24 09:29:24 LOG7[0]: TLS alert (write): fatal: decode error 2024.01.24 09:29:24 LOG6[0]: TLS socket closed (SSL_read) 2024.01.24 09:29:24 LOG7[0]: Sent socket write shutdown 2024.01.24 09:29:24 LOG5[0]: Connection closed: 1755 byte(s) sent to TLS, 634 byte(s) sent to socket 2024.01.24 09:29:24 LOG7[0]: Remote descriptor (FD=896) closed 2024.01.24 09:29:24 LOG7[0]: Local descriptor (FD=892) closed 2024.01.24 09:29:24 LOG7[0]: Service [afip-prod-fce] finished (0 left) Thank you! Kind regards, Rodrigo.

3 3

stunnel warning: SSL_accept: ../ssl/record/ssl3_record.c:354: error:0A00010B:SSL routines::wrong version number
by Marcel de Rooy 23 Jan '25

23 Jan '25

Hi, Taking this opportunity to ask a question on the mentioned warning. In our stunnel setup (stunnel server in a Docker container on Linux, version 5.68 and windows clients on version 5.73, no certificate verification) I am seeing every minute the following lines in stunnel.log on the server side: 2025.01.20 04:12:27 LOG5[0]: Service [siptest] accepted connection from 172.20.23.1:46658 2025.01.20 04:12:27 LOG3[0]: SSL_accept: ../ssl/record/ssl3_record.c:354: error:0A00010B:SSL routines::wrong version number 2025.01.20 04:12:27 LOG5[0]: Connection reset: 0 byte(s) sent to TLS, 0 byte(s) sent to socket This is every minute, so 04:13:27 again, etc. The warning is there already shortly after container restart without active connections to our SIP devices. I only see it recently. And changing the server/client config with sslVersionMin = TLSv1.2 and sslVersionMax = TLSv1.3 did not resolve it. Since it comes back every minute, I was thinking in the direction of keepalive settings. But do keep alives need encryption? Probably not. Is this just an innocent bug in the stunnel code or could I still do something in my configuration to clear the warn? Thank you for your attention. Marcel de Rooy Rijksmuseum Netherlands xxx

3 4

How do I setup stunnel + openvpn for android (I already have the server running, I just need a android client, Sslsocks isn't working for some reason for me.)
by sharifkashif224＠gmail.com 23 Jan '25

23 Jan '25

I've tried using Sslsocks but it keeps giving me an error called unexpected eof while reading. This occurs when I try to initiate a connection via OpenVPN in android.

1 0