iDefense Security Advisory 05.07.08
http://labs.idefense.com/intelligence/vulnerabilities/
May 07, 2008

I. BACKGROUND

rdesktop is an open source client that speaks the Remote Desktop
Protocol (RDP). This allows Unix-based users to login to Windows
Terminal Servers. More information is available at the following URL.

http://www.rdesktop.org/

II. DESCRIPTION

Remote exploitation of an integer signedness vulnerability in rdesktop,
as included in various vendors' operating system distributions, allows
attackers to execute arbitrary code with the privileges of the
logged-in user.

The vulnerability exists within the code responsible for reallocating
dynamic buffers. The rdesktop xrealloc() function uses a signed
comparison to determine if the requested allocation size is less than
1. When this occurs, the function will incorrectly set the allocation
size to be 1. This results in an improperly sized heap buffer being
allocated, which can later be overflowed.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the logged in user. In order to exploit this
vulnerability, an attacker must persuade a targeted user to connect to a
malicious RDP server.

IV. DETECTION

iDefense confirmed the existence of this vulnerability in rdesktop
version 1.5.0. Previous versions may also be affected.

V. WORKAROUND

iDefense is currently unaware of any effective workaround for this
issue.

VI. VENDOR RESPONSE

The rdesktop maintainer has addressed this vulnerability with CVS
revision 1.162 of rdesktop.c. For more information, visit the following
URL.

http://rdesktop.cvs.sourceforge.net/rdesktop/rdesktop/rdesktop.c?view=diff&pathrev=HEAD&r1=text&tr1=1.162&r2=text&tr2=1.118&diff_format=h#l1134

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-1803 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

11/12/2007  Initial vendor notification
11/19/2007  Initial vendor response
05/07/2008  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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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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