Citrix Program Neighborhood Name Heap Corruption Vulnerability iDefense Security Advisory 12.16.05 www.idefense.com/application/poi/display?id=357&type=vulnerabilities December 16, 2005 I. BACKGROUND Citrix Program Neighborhood is the client used to connect to applications published on Citrix Metaframe servers. More information is available from the vendor website: http://www.citrix.com II. DESCRIPTION Remote exploitation of a heap overflow vulnerability in Citrix, Inc.'s Program Neighborhood allows attackers to execute arbitrary code. The vulnerability specifically exists due to insufficient handling of corrupt Application Set responses. A heap-based buffer overflow will occur when the Citrix Program Neighborhood client receives an Application Set response containing a name value over 286 bytes. The overflow will trigger an access violation in RtlFreeHeap() with register control sufficient to write 4 bytes to an arbitrary location as shown below: 77F52A7B 8B4E 0C MOV ECX,DWORD PTR DS:[ESI+C] 77F52A7E 898D 60FFFFFF MOV DWORD PTR SS:[EBP-A0],ECX 77F52A84 8901 MOV DWORD PTR DS:[ECX],EAX Registers: EAX 41414141 ECX 00004141 ESI 008D5E30 ASCII "AAAAAAAAAAAAAA" EIP 77F52A84 ntdll.77F52A84 Crash: 77F52A84 8901 MOV DWORD PTR DS:[ECX],EAX Remote attackers can send an specially crafted name value to overflow the buffer and execute arbitrary code. III. ANALYSIS Successful exploitation of the vulnerability allows remote attackers to execute arbitrary code with user privileges. The overflow is a trivial heap-based buffer overflow due to insufficient bounds checking on the 'name' value in Application Set responses. A typical exploitation scenario would require an attacker to setup a fake Citrix Server and wait for a Citrix Program Neighborhood client to connect. Upon receiving the first connecting packets from the client, the server would send a corrupt UDP packet to the client. IV. DETECTION iDefense has confirmed the existence of this vulnerability in Citrix Presentation Server Client 9.0. All prior versions are suspected vulnerable. V. WORKAROUND iDefense is unaware of any effective workarounds at this time. VI. VENDOR RESPONSE The vendor has released the following advisory to address this issue: http://support.citrix.com/kb/entry.jspa?externalID=CTX108354 VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2005-3652 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 11/15/2005 Initial vendor notification 11/15/2005 Initial vendor response 12/16/2005 Coordinated public disclosure IX. CREDIT iDefense credits Patrik Karlsson (patrik (at) cqure (dot) net [email concealed]) with the discovery of this vulnerability. Get paid for vulnerability research http://www.iDefense.com/poi/teams/vcp.jsp Free tools, research and upcoming events http://labs.iDefense.com X. LEGAL NOTICES Copyright © 2005 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 part of this alert in any other medium other than electronically, please email customerservice (at) iDefense (dot) com [email concealed] 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.