Multiple Vendor GTK+ gdk-pixbuf XPM Loader Heap Overflow Vulnerability

iDEFENSE Security Advisory 11.15.05
www.idefense.com/application/poi/display?id=339&type=vulnerabilities
November 15, 2005

I. BACKGROUND

GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Offering a complete set of widgets, GTK+ is suitable for projects
ranging from small one-off projects to complete application suites.

II. DESCRIPTION

Remote exploitation of heap overflow vulnerability in various vendors'
implementations of the GTK+ gdk-pixbuf XPM image rendering library could
allow for arbitrary code execution.

The vulnerability specifically exists due to an integer overflow while
processing XPM files. The following code snippet illustrates the
vulnerability:

if (n_col <= 0 || n_col >= G_MAXINT / (cpp + 1)) {
                g_set_error (error,
                             GDK_PIXBUF_ERROR,
                             GDK_PIXBUF_ERROR_CORRUPT_IMAGE,
                             _("XPM file has invalid number of colors"));
        return NULL;
    }
[...]
colors = (XPMColor *) g_try_malloc ((sizeof (XPMColor) * n_col));
[...]


The validity check of n_col is enough to prevent an integer overflow in
the first g_try_malloc, however there is not a proper check for the
second g_try_malloc, which allows an undersized heap buffer to be
allocated, then overflowed while using n_col as an upper bounds in a
copying loop. This can be used to execute arbitrary code via traditional
heap overflow 4 byte write methods or by overwriting adjacent areas of
the heap with important values such as function pointers.

III. ANALYSIS

Exploitation could allow for arbitrary code execution in the context of
the user running the affected application. As this library is used in a
variety of applications, this vulnerability could be exploited either
remotely, via a networked application or locally.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in gtk+ 2.4.0
compiled from source. It is suspected that previous versions are also
affected by this vulnerability. The following vendors include
susceptible GTK+ and GdkPixBuf packages within their respective
operating system distributions:

    The Debian Project:
      Debian GNU/Linux 3.0 and 3.1 (all architectures)
    Mandriva (formerly Mandrakesoft):
      Mandriva Linux (formerly Mandrakelinux) 10.0 and 10.1,
      Corporate Server 3.0
    Novell Inc.:
      SuSE Linux 8.2, 9.0, 9.1 and 9.2
    Red Hat Inc.:
      Red Hat Enterprise Linux 2.1, 3, 4,
      Fedora Core 3, 4

V. WORKAROUND

Users should not open untrusted media files.

VI. VENDOR RESPONSE

Red Hat Inc.:

"This issue affects the gtk2 packages as shipped with Red Hat Enterprise
Linux 3 and 4, and the gdk-pixbuf packages as shipped with Red Hat
Enterprise Linux 2.1, 3, and 4.  Updates to these packages are available
at the URL below or by using the Red Hat Network up2date tool.
http://rhn.redhat.com/errata/CVE-2005-3186.html

This issue affects the gtk2 and gdk-pixbuf packages as shipped with
Fedora Core 3 and 4."

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-3186 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

10/12/2005  Initial vendor notification
10/14/2005  Initial vendor response
11/15/2005  Coordinated public disclosure

IX. CREDIT

infamous41md is credited with the discovery of this vulnerability.

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X. LEGAL NOTICES

Copyright © 2005 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.