Microsoft Windows contains a vulnerability in the Telnet service that could allow an unauthenticated, remote attacker to execute arbitrary code.
This vulnerability exists due to insufficient protections on credential reuse attacks. An unauthenticated, remote attacker could exploit this vulnerability by convincing a user to connect to a malicious Telnet server. If successful, the attacker could execute arbitrary code with the privileges of the user.
Microsoft has confirmed this vulnerability in a security bulletin and released software updates that correct it.
Indicators of Compromise
The following Microsoft systems are affected:
Windows 2000 SP4 and prior
Windows XP SP3 and prior
Windows XP Professional x64 Edition SP2 and prior
Windows Server 2003 SP2 and prior
Windows Server 2003 x64 Edition SP2 and prior
Windows Server 2003 for Itanium-based Systems SP2 and prior
Windows Vista SP2 and prior
Windows Vista x64 Edition SP2 and prior
Windows Server 2008 for 32-bit Systems SP2 and prior
Windows Server 2008 for x64-based Systems SP2 and prior
Windows Server 2008 for Itanium-based Systems SP2 and prior
This vulnerability exists due to insufficient protections on credential reuse attacks. The Telnet protocol does not use NTLM credential-reflection protections. As a result, an unauthenticated, remote attacker could attempt to reuse a user's credentials against the vulnerable system by convincing a user to visit a malicious Telnet server. If successful, the attacker could execute arbitrary code on the user's system with the privileges of the user.
Attackers cannot directly exploit this vulnerability and instead rely upon user participation in order to accomplish an exploit. A user must first visit a malicious Telnet server. An attacker may provide links within e-mail messages designed to open a Telnet session to a malicious host. If successful, the attacker could replay the user's credentials against the vulnerable system, allowing the attacker to execute arbitrary code with the privileges of the user.
In addition to release patches, Microsoft has also released updates for Windows 7; however, this software is still in beta and not recommended for production use.
The update available from Microsoft corrects this vulnerability by implementing proper credential protections.
Administrators are advised to apply the available software updates.
Administrators are advised not to connect to unknown systems using Telnet.
Administrators are advised to monitor critical systems.
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: MS09-042
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.