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 underflow 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 reading in an
RDP request. When reading a request, a 16-bit integer value that
represents the number of bytes that follow is taken from the packet.
This value is then decremented by 4, and used to calculate how many
bytes to read into a heap buffer. The subtraction operation can
underflow, which will then lead to the heap buffer being 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 1.20 of iso.c. For more information, visit the following URL.

http://rdesktop.cvs.sourceforge.net/rdesktop/rdesktop/iso.c?annotate=1.20&diff_format=h&pathrev=HEAD#l101

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-1801 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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