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Citrix Program Neighborhood Agent Arbitrary Shortcut Creation Vulnerability

04.26.05

BACKGROUND

Citrix Program Neighborhood Agent is a part of the Citrix Presentation
Server Client and facilitates access to Citrix published applications.

DESCRIPTION

Remote exploitation of a design error in Citrix Systems Inc.'s Program
Neighborhood Agent allows attackers to create arbitrary shortcuts under
the privileges of the client user.

Citrix Program Neighborhood Agent is a part of the Citrix Presentation
Server Client and facilitates access to Citrix published applications.
The problem specifically exists in that an attacker who has established
a malicious server can create arbitrary shortcuts to the client user's
Startup folder by specifying the following directive:

   <AppInStartmenu value="true" root="programs">startup</AppInStartmenu>

An attacker can specify the UNC path to an arbitrary malicious binary,
and this binary will be executed the next time the client user reboots
with an active network connection.

ANALYSIS

Successful exploitation allows remote attackers to execute arbitrary
code under the privileges of the client user. Exploitation requires that
an attacker establish a malicious server and cause or convince the
target user to connect to it via the Program Neighborhood Agent. This
can be accomplished by social engineering or automatically when combined
with a DNS- or ARP-spoofing attack.

DETECTION

iDEFENSE has confirmed the existence of this vulnerability in Citrix
MetaFrame Program Neighborhood v8.00.24737. It is suspected that earlier
versions are also vulnerable.

WORKAROUND

Utilize the server IP address instead of the name to circumvent DNS
spoofing attacks.

VENDOR RESPONSE

A vendor advisory for this vulnerability is available at:
   http://support.citrix.com/kb/entry.jspa?externalID=CTX105650

Updated clients to address this vulnerability are available at:
   http://www.citrix.com/English/SS/downloads/downloads.asp?dID=2755

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2004-1077 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

11/23/2004    Initial vendor notification
11/24/2004    Initial vendor response
04/26/2005    Coordinated public disclosure

CREDIT

Patrik Karlsson (cqure.net) is credited with this discovery.

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LEGAL NOTICES

Copyright © 2005 Verisign, 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
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for 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.