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Date: Wed, 01 Jun 2011 10:27:43 +0200
From: Matthias Andree <>
Subject: Re: CVE request for fetchmail STARTTLS hang (Denial
 of Service)

Am 31.05.2011 22:41, schrieb Matthias Andree:
> Am 31.05.2011 22:01, schrieb Josh Bressers:
>> ----- Original Message -----
>>> Could I get a CVE name for the issue in
>>> <>?
>> Please use CVE-2011-1947.
> Thanks.
>> I can't help but wonder what else could be vulnerable to a similar flaw.
>> Has anyone looked?
> I seriously considered not asking for a CVE in the first place because
> it's rather close to a resource-hogging-through-slowdowns attack vector,
> if you send at a very slow pace just avoiding the timeout by a notch,
> you hog your peer's resources for extended amounts of time -- and I
> can't think of good heuristics to tell abuse from legit use by those on
> slow links apart, and it's pointless listing CVEs for the unfixable
> situations.
> Anecdotal story from the fix: I've been particularly disappointed that
> Solaris 10 doesn't support setsockopt(n, SOL_SOCKET, SO_RCVTIMEO, &foo,
> sizeof foo); (returns -1 with errno == EAFNOSUPPORT), which would have
> been the thorough and easy way out.  I've had the code in place and
> released as candidate, but umm, no, didn't work. I do set SO_KEEPALIVE
> now, but that's not anywhere close of defending against malice.

I wrote too fast.
Just so that the list archives reflect the actual fix:

The fixed fetchmail version 6.3.20 runs the SSL_connect() [OpenSSL]
under a real-time setitimer() that triggers SIGALRM after a
user-configurable setting (default 300 s).

SO_KEEPALIVE takes more than two hours on some systems' defaults before
even sending the first TCP keepalive probe, which is too long, but can
be tuned through sysctl or ndd on many relevant systems -- and, more
importantly, bears no relation to what happens up in the application
layer. That's what I meant with "does not defend against malice" (for
instance, a server deliberately keeping the TCP connection open without
responding), and that situation is what the real-time setitimer() will

Matthias Andree

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