[stunnel-users] Problem with sslv2 clients

Sat Dec 10 14:26:48 CET 2011

Sorry, my mistake for not being clearer: I do not want to use SSLv2, I 
want the automatic negotiation to work. The client does not get any kind 
of response from stunnel, instead, the TCP connection is closed! (RST 
packet)

I'm no expert for ssl, but it looks to me, like the client tried SSLv2 
first, but offered TLSv1 also (please see screenshot of packet trace in 
my first mail). The server did not answer with it's capabilities, but 
simply closed the connection.

Is this really normal? Shouldn't stunnel answer, in protocol, that it 
only supports certain other encryption methods?

Greetings
Markus Borst

Am 09.12.2011 19:14, schrieb Ludovic LEVET:
> Hi,
>
> Normal, SSLv2 is disable by default since version 4.40. 
> (http://www.stunnel.org/?page=sdf_ChangeLog)
> To re-enable it add in your config file :
>
> ciphers = ALL:!aNULL:!EXP:!LOW:-MEDIUM:RC4:+HIGH  (or other)
> and
> sslVersion = all
>
>
> Ludovic.
>
>
>
>>
>>
>>
>> Le 09/12/2011 15:37, Markus Borst a écrit :
>>> Hi,
>>>
>>> we have a strange problem with newer stunnel versions (4.50 on 
>>> windows), compared to older ones (known to work is version 4.35). 
>>> The problem seems to be, that if a client sends a SSLv2 Helo 
>>> message, the stunnel server simply resets the TCP connection, 
>>> without trying to negotioate anything.
>>>
>>> Setup: Stunnel is used top provide ssl/tls for imap, Hobbit is used 
>>> to monitor service availability. The Hobbit module to monitor imaps 
>>> seems to try SSLv2 first, but also supports newer versions (SSLv3 
>>> and TLSv1). The ssl connection never gets established, stunnel sends 
>>> a tcp RST, hobbit never retries. We can force some hobbit modules to 
>>> use TLSv1 exclusively, but not all of them. We fear that some older 
>>> mailclients will also have problems initiating a connection, so we 
>>> keep stunnel 4.35 running for now.
>>>
>>> stunnel.conf:
>>>
>>> fips = no
>>> debug = 7
>>> output = stunnel.log
>>>
>>> [imaps]
>>> accept  = 130.83.174.1:993
>>> connect = 127.0.0.1:143
>>> cert    = imap.xxx.company.yy.pem
>>>
>>>
>>> stunnel.log:
>>>
>>> 2011.12.09 14:55:12 LOG5[6820:2144]: Service imaps accepted 
>>> connection from xxx.yyy.zzz.105:45294
>>> 2011.12.09 14:55:12 LOG3[6820:2144]: SSL_accept: 1408F10B: 
>>> error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number
>>> 2011.12.09 14:55:12 LOG5[6820:2144]: Connection reset: 0 bytes sent 
>>> to SSL, 0 bytes sent to socket
>>> 2011.12.09 14:55:12 LOG7[6820:2144]: Service imaps finished (0 left)
>>> 2011.12.09 14:55:12 LOG7[6820:2144]: str_stats: 0 block(s), 0 data 
>>> byte(s), 0 control byte(s)
>>>
>>>
>>>
>>> Wireshark Packet Trace (see attached image).
>>>
>>>
>>> What's wrong here? Shouldn't client and server negotiate the methods 
>>> used? The client seems to offer TLS ("Version: TLS 1.0 ..."), but 
>>> instead of negotiating, the server simply closes the connection.
>>>
>>>
>>> Greetings
>>> Markus Borst
>>>
>>
>
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-- 

TU Darmstadt
Hochschulrechenzentrum (HRZ)
Markus Borst
S4/14/2.4.06
Adresse:     Mornewegstr. 30   64293 Darmstadt
Tel.:     06151/16-2056
Email:     M.Borst at hrz.tu-darmstadt.de