Effective 2019 Sep 15, Cisco will no longer publish non-Cisco product alerts. Cisco will continue to publish Security Advisories to address third-party software vulnerabilities per the Cisco Security Vulnerability Policy.
Multivendor Vulnerability Alert
Microsoft Windows WinVerifyTrust Function Authenticode Signature Verification Bypass Vulnerability
A vulnerability in the WinVerifyTrust function of Microsoft Windows could allow an unauthenticated, remote attacker to execute arbitrary code on a targeted system.
The vulnerability is due to improper verification of the contents of signed executable files. An unauthenticated, remote attacker could exploit this vulnerability by manipulating the contents of a signed executable file. Successful exploitation could allow the attacker to bypass security validation and possibly execute arbitrary code on a targeted system.
Microsoft has confirmed the vulnerability in a security bulletin and released software updates.
Indicators of Compromise
The following Microsoft Windows systems are affected:
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 with SP2 and prior for Itanium-based Systems
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
Windows 7 for 32-bit Systems SP1 and prior
Windows 7 for x64-based Systems SP1 and prior
Windows Server 2008 R2 for x64-based Systems SP1 and prior
Windows Server 2008 R2 for Itanium-based Systems SP1 and prior
Windows 8.1 for 32-bit Systems
Windows 8.1 for x64-based Systems
Windows Server 2012
Windows Server 2012 R2
Windows RT 8.1
The vulnerability is due to improper validation of the contents of signed executable files by the WinVerifyTrust function in Microsoft Windows. The function improperly verifies digest contents in Portable Executable (PE) files.
An unauthenticated, remote attacker could exploit the vulnerability by manipulating the contents of a legitimate PE file. The attacker could embed malicious instructions while maintaining the integrity of the signature. When the executable file runs on an affected system, the system incorrectly verifies the signature as valid. The attacker could use this behavior to supply malicious executable files that may be trusted by a system user. If successful, the attacker could execute arbitrary code on the system with the privileges of the user.
Exploitation of this vulnerability depends on user interaction. An attacker can manipulate the contents of an executable file, but the attacker must still deliver and convince a system user to open the executable. The integrity of the digital signature may increase the likelihood that the user trusts the executable because the system may display the source of the executable as a trusted third party.
Administrators are advised to apply the appropriate updates.
Users are advised not to open email messages from suspicious or unrecognized sources. If users cannot verify that links or attachments included in email messages are safe, they are advised not to open them.
Administrators are advised to monitor affected 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: MS13-098
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 Microsoft Update service. 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.