Additional technical information is available for the Microsoft Windows Remote Desktop Connection arbitrary code execution vulnerability.
Description
Microsoft Windows contains a vulnerability in Remote Desktop Connection that could allow an unauthenticated, remote attacker to gain complete control over an affected system.
The vulnerability exists because of a heap overflow vulnerability in Remote Desktop Connection. If an attacker can convince a user to connect to a malicious Remote Desktop Protocol (RDP) server, the attacker can execute arbitrary code on the client machine with the privileges of the user.
Microsoft has acknowledged this vulnerability in a security bulletin and has released software updates that correct it.
Warning Indicators
The following systems are affected:
Microsoft Windows 2000 SP4 and prior
Microsoft Windows XP SP3 and prior
Microsoft Windows XP Professional x64 Edition SP2 and prior
Microsoft Windows Server 2003 SP2 and prior
Microsoft Windows Server 2003 for Itanium-based Systems with SP2 and prior
Microsoft Windows Vista SP1 and prior
Microsoft Windows Vista x64 Edition SP1 and prior
Microsoft Windows Server 2008 for 32-bit Systems SP2 and prior
Microsoft Windows Server 2008 for x64-based Systems SP2 and prior
Microsoft Windows Server 2008 for Itanium-based Systems
Macintosh OS X Systems using Microsoft Remote Desktop Connection Client for Mac version 2
IntelliShield Analysis
This vulnerability requires an attacker to convince a user to connect to a malicious system. An attacker might exploit this vulnerability by convincing an administrator that the malicious system is instead a system that requires remote assistance, employing a man-in-the-middle attack between the user and a legitimate system, or using a web-based attack through the Remote Desktop ActiveX control.
The Cisco Applied Intelligence team has created an Applied Mitigation Bulletin to address vulnerabilities that Microsoft disclosed in the August 2009 security bulletin release. This Cisco bulletin, which assists administrators in identifying or mitigating these vulnerabilities using Cisco devices, is available at the following link: Cisco Applied Mitigation Bulletin: Microsoft Security Bulletin Release for August 2009
Microsoft has corrected this vulnerability by improving the handling of unexpected parameters sent by the RDP server.
Vendor Announcements
Microsoft has released a security bulletin at the following link: MS09-044
Impact
An unauthenticated, remote attacker could exploit this vulnerability to execute arbitrary code on an affected system. The attacker can execute code with the privileges of the user who is running the Remote Desktop Connection. If the user holds Administrator privileges, the attacker could gain complete control over the affected system.
Technical Information
The vulnerability exists on affected systems because Remote Desktop Connection does not properly handle memory when receiving parameters from a malicious RDP server. The vulnerability exists in the client-side mstscax.dll library when parsing packets from the RDP server. The vulnerability allows the malicious RDP server to write to arbitrary memory within the connection process memory space. The attacker can use this to execute arbitrary code with the privileges of the account invoking the Remote Desktop Connection software.
Attackers may also use a malicious web page to invoke the Remote Desktop Connection ActiveX control, which also suffers from this vulnerability. In this attack vector, the victim may be enticed to follow a link to a malicious page through an e-mail message, instant messenger conversation, social networking site, or other web-enabled medium.
This vulnerability does not affect Remote Desktop Connection server code, only client code.
Safeguards
Administrators are advised to apply the appropriate updates.
Users are advised not to open e-mail messages from suspicious or unrecognized sources. If users cannot verify that links or attachments included in e-mail messages are safe, they are advised not to open them.
Administrators are advised to implement an intrusion prevention system (IPS) or intrusion detection system (IDS) to help detect and prevent attacks that attempt to exploit this vulnerability.
Administrators may consider using the Microsoft Baseline Security Analyzer (MBSA) scan tool to identify common security misconfigurations and missing security updates on system endpoints.
Patches/Software
Microsoft customers can obtain updates directly by using the links in the security bulletin. These updates are also distributed by Windows automatic update features and available on the Windows Update website. Microsoft Windows Server Update Services (WSUS), Systems Management Server, and System Center Configuration Manager can assist administrators in deploying software updates.
Signatures
Cisco Systems Cisco Intrusion Prevention System (IPS) 6.0
Version 1, August 11, 2009, 2:32 PM: Microsoft Windows Remote Desktop Connection contains a vulnerability that could allow an unauthenticated, remote attacker to gain complete control over an affected system. Updates are available.
Original Release Base, SP1 | Professional Edition Base, SP1, SP2, SP3 | Professional Edition, 64-bit (Itanium) 2003 (itanium 2), Base, SP1, SP2 | Professional x64 (AMD/EM64T) Base, SP1, SP2
Associated Products:
N/A
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