iDefense Security Advisory 10.09.08
http://labs.idefense.com/intelligence/vulnerabilities/ 
Oct 09, 2008

I. BACKGROUND

The Common UNIX Printing System, more commonly referred to as CUPS,
provides a standard printer interface for various Unix based operating
systems. "imagetops" is a part of CUPS responsible for creating
PostScript representations of different graphic file formats. For more
information, visit the vendor's website at the following URL.

http://www.cups.org/ 

II. DESCRIPTION

Remote exploitation of a heap-based buffer overflow vulnerability in
CUPS, as included in various vendors' operating system distributions,
could allow an attacker to execute arbitrary code with the privileges
of the affected service.

The Common Unix Printing System, more commonly referred to as CUPS,
provides a standard printer interface for various Unix-based operating
systems.

The Silicon Graphics Image (SGI) file format parsing module is
vulnerable to a heap-based buffer overflow vulnerability when parsing
malformed Run Length Encoded (RLE) data. The vulnerability exists
within the read_rle16() function. This function doesn't correctly
validate the row count value taken from the file, which is then used to
control how many 16-bit integers to store into a heap-based buffer. By
providing small image dimensions and a large row count, it is possible
to trigger a heap-based buffer overflow.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the affected service. Depending on the
underlying operating system and distribution, CUPS may run as the lp,
daemon or a different user.

Exploiting heap overflow vulnerabilities on modern Unix systems can be
difficult due to various heap protection schemes; however, the attacker
has very fine-grained control over the overflow, which somewhat eases
the difficulty of exploitation.

To exploit this vulnerability remotely, the targeted host must be
sharing a printer(s) on the network. If a printer is not being shared,
CUPS only listens on the localhost interface, and the scope of this
vulnerability would be limited to local privilege escalation.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in CUPS
version 1.3.7. Previous versions may also be affected.

V. WORKAROUND

Disabling printer sharing will prevent this vulnerability from being
exploited remotely; however, local exploitation is still possible.

VI. VENDOR RESPONSE

CUPS.org has released a patch which addresses this issue. For more
information, consult their advisory at the following URL.

http://www.cups.org/str.php?L2918 

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

09/02/2008  Initial Vendor Notification
10/09/2008  Public Disclosure

IX. CREDIT

This vulnerability was reported to iDefense by regenrecht.

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X. LEGAL NOTICES

Copyright =A9 2008 iDefense, Inc.

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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
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