GnuPG 1.4 and 2.0 buffer overflow

Advisory Content :

GnuPG 1.4 and 2.0 buffer overflow
==================================

Summary
=======

While fixing a bug reported by Hugh Warrington, a buffer overflow has
been identified in all released GnuPG versions. The current versions
1.4.5 and 2.0.0 are affected. A small patch is provided.

Please do not send private mail in response to this message. The
mailing list gnupg-devel is the best place to discuss this problem
(please subscribe first so you don't need moderator approval [1]).

Impact
======

When running GnuPG interactively, special crafted messages may be used
to crash gpg or gpg2. Running gpg in batch mode, as done by all
software using gpg as a backend (e.g. mailers), is not affected by
this bug.

Exploiting this overflow seems to be possible.

gpg-agent, gpgsm, gpgv or other tools from the GnuPG suite are not
affected.

Solution
========

Apply the following patch to GnuPG. It should apply cleanly to
current versions (1.4.5 as well as 2.0.0) but might also work for
older versions.

2006-11-27 Werner Koch <wk (at) g10code (dot) com [email concealed]>

* openfile.c (ask_outfile_name): Fixed buffer overflow occurring
if make_printable_string returns a longer string. Fixes bug 728.

--- g10/openfile.c (revision 4348)
+++ g10/openfile.c (working copy)
@@ -144,8 +144,8 @@

s = _("Enter new filename");

- n = strlen(s) + namelen + 10;
defname = name && namelen? make_printable_string( name, namelen, 0):
NULL;
+ n = strlen(s) + (defname?strlen (defname):0) + 10;
prompt = xmalloc(n);
if( defname )
sprintf(prompt, "%s [%s]: ", s, defname );

Background:
===========

The code in question has been introduced on July 1, 1999 and is a
pretty obvious bug. make_printable_string is supposed to replace
possible dangerous characters from a prompt and returns a malloced
string. Thus this string may be longer than the orginal one; the
buffer for the prompt has only be allocated at the size of the original
string - oops. Note, that using snprintf would not have helped in
this case. How I wish C-90 had introduced asprintf or at least it
would be available on more platforms.

The original bug report is at https://bugs.g10code.com/gnupg/issue728 .

===
[1] See http://lists.gnupg.org/mailman/listinfo/gnupg-devel .

--
Werner Koch <wk (at) gnupg (dot) org
[email concealed]>
The GnuPG Experts http://g10code.com
Join the Fellowship and protect your Freedom! http://www.fsfe.org
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.1rc1 (GNU/Linux)

iEYEARECAAYFAkVrHJ4ACgkQYHhOlAEKV+3OKQCgq2DZx5xez/033RhUOUy/9ElZ
FLAAnAsIc+zYjmjvo5N8rmVtVdejeLKa
=29PW
-----END PGP SIGNATURE-----

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GnuPG 1.4 and 2.0 buffer overflow