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Date: Fri, 17 Apr 2015 13:23:27 -0400
From: Rich Felker <>
To: Matt Johnston <>
Subject: Re: Re: Security advisory for musl libc - stack-based buffer
 overflow in ipv6 literal parsing [CVE-2015-1817]

On Fri, Apr 17, 2015 at 09:10:08PM +0800, Matt Johnston wrote:
> Hi,
> I think Dropbear probably is vulnerable to CVE-2015-1817
> post-authentication. TCP forwarding requests will call
> getaddrinfo() 
> (moved to netio.c in head, and PF_UNSPEC has been fixed to
> AF_UNSPEC). Pre-authentication should be OK, only
> getnameinfo() is called (if that's enabled).

Yes, I agree dropbear is affected.

And wow, this is an utter mess. Not only does dropbear fail to drop
root before processing forwards; it NEVER drops root at all. The
user's session remains running as root for its full lifetime. Aside
from being a huge risk, it also allows users to bypass uid-based
firewall rules via port forwarding; for example, a rule that forbids
normal users from making outgoing connections on port 25 would not be

Is there any reason for not performing the setgroups/setgid/setuid
immediately after authentication succeeds? Have you looked at whether
it would be easy to patch that in?

None of this excuses CVE-2015-1817 which was a huge failure on our
part, but it seems pretty crazy that dropbear is doing EVERYTHING as

> musl's network-facing DNS code seems a bit precarious with
> pointer arithmetic?

Which code are you talking about? There was a previous problem with
dn_expand, which is the main function that comes to mind for me, and
the code was fixed and heavily reviewed at the time.

Are there other areas you're concerned about?


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