oss-security - Re: debian: gpg --verify suggests entire file was verified, even if file contains auxiliary data

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Message-ID: <516EE889.4090604@redhat.com>
Date: Wed, 17 Apr 2013 12:23:05 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: Thomas Biege <thomas@...e.de>
Subject: Re: debian: gpg --verify suggests entire file was
 verified, even if file contains auxiliary data

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 04/17/2013 03:54 AM, Thomas Biege wrote:
> Hi, this might possibly need a CVE-ID. 
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=704645 
> https://bugs.g10code.com/gnupg/issue1486
> 
> 
> Itself it might be no issue but in conjunction with other
> applications this could become a vulnerability.
> 
> Bye, Thomas

I've run into this before, sadly enigmail (Thunderbird gpg plugin)
displays the same green bar for message signed ok, but displays the
text as "Part of the message signed" so unless you're really paying
attention, you'll miss it.

My thinking is this:

1) It's pretty easy to find signed content for people using GPG
2) It's pretty easy to append/embed signed content into a larger message

So the attack would be: create malicious content/email, embed/append a
valid message harvested from somewhere. Send to user. The user
verifies then reads the message, unless they are really paying
attention they probably won't notice that the content isn't signed
properly (e.g. have an email, ton of whitespace, then the signed
message). Personally I'm inclined to assign a CVE, enigmail for
example does mostly the right thing (makes a distinction between fully
signed and partially signed). I think GPG should too.
Thoughts/comments before I assign this?

- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993
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