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Date: Sat, 18 Apr 2015 20:27:37 +0200
From: Laurent Bercot <>
Subject: Re: Re: Security advisory for musl libc - stack-based buffer
 overflow in ipv6 literal parsing [CVE-2015-1817]

On 18/04/2015 19:07, Harald Becker wrote:
> AFAIK, you use a CNAME as MX, which is resolved on some, but not all
> systems / programs. You need to add an absolute IP address for your
> MX, not a CNAME, to be accessible for all.

  Indeed. The normative text is RFC 2181, section 10.3 : it explicitly
forbids MX targets to be a CNAME. Most modern MTAs don't care, but some
old ones *cough* sendmail *cough* do.

> I didn't think of an exec to a separate program, but just fork and
> let a process for key management run in the back. So a bit simpler to
> verify authentication of caller, but still somehow required ... or
> what else did you suggest?

  I second the fact that forking several communicating processes at start,
each process dropping privileges to the minimal amount required to do its
job, is the most secure design.
  (That's how qmail was designed, way back in 1996, and it's definitely the
right approach for secure Unix programming.)
  If there's interest in converting dropbear to that model, I'd be happy
to help.


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