Public Vulnerability Reports

Multiple Vendor rdesktop channel_process() Integer Signedness Vulnerability

07.05.08

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/

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.

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.

DETECTION

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

WORKAROUND

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

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

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.

DISCLOSURE TIMELINE

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

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2008 Verisign, Inc.

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