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.
Permission is granted for the redistribution of this alert electronically. It may not be edited in
any way without the express written consent of iDefense. If you wish to reprint the whole or any
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permission.
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.
