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. "texttops" is a part of CUPS responsible for creating
PostScript representations of text files. For more information, visit
the vendor's website at the following URL.

http://www.cups.org/

II. DESCRIPTION

Remote exploitation of an integer 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 vulnerability exists within the WriteProlog() function in the
"texttops" application. When calculating the page size used for storing
PostScript data, multiple values that are derived from
attacker-controlled content are used in a multiplication operation.
This calculation can overflow, resulting in an incorrect result for the
total page size. This value is then used to allocate a heap buffer that
is later filled with attacker controlled content, resulting in a heap
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, iDefense has
proof-of-concept exploit code that demonstrates code execution is
possible.

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?L2919

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 © 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
of the information constitutes acceptance for use in an AS IS condition.
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