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.
Indicators of Compromise
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
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.
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.
Microsoft has corrected this vulnerability by improving the handling of unexpected parameters sent by the RDP server.
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.
Microsoft has released a security bulletin at the following link: MS09-044
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.
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Cisco Multivendor Vulnerability Alerts respond to vulnerabilities identified in third-party vendors' products. These alerts contain information compiled from diverse sources and provide comprehensive technical descriptions, objective analytical assessments, workarounds and practical safeguards, and links to vendor advisories and patches.