WinVerifyTrust Signature Validation CVE‐2013‐3900 Mitigation

Overview

The CVE-2013-3900 vulnerability pertains to a flaw in the WinVerifyTrust signature validation function in Windows operating systems. This vulnerability can be exploited to execute remote code by bypassing security features intended to verify the integrity and origin of signed executables and scripts.

• Severity: High

Impact

Exploiting this vulnerability can lead to:

• Remote Code Execution: Malicious actors can execute arbitrary code on a victim's system by spoofing the signature of trusted software.
• Breach of Trust: The integrity of system and application updates or installations could be compromised, leading to further security breaches.
• Elevation of Privilege: If exploited by other malware, it can lead to elevated privileges within the system.

Cause

This vulnerability is caused by improper handling of certain types of signatures by the WinVerifyTrust function, which fails to properly verify the authenticity of certain signatures, thus allowing tampered or maliciously crafted files to appear as trusted.

Solution

To mitigate this vulnerability and enhance system protection against potential exploits:

1. Apply Security Updates:
   • Immediately apply all available Windows updates that address this vulnerability. Microsoft has released patches that correct the way WinVerifyTrust handles signatures.
   • Enable Windows Update to automatically download and install future patches.
2. Enable Certificate Verification:
   • Configure Group Policy settings to enforce stricter certificate validation: Computer Configuration > Administrative Templates > System > Internet Communication Management > Internet Communication settings > Turn off Automatic Root Certificates Update: Disabled
3. Monitor and Audit:
   • Regularly monitor systems for unusual application behavior that might indicate an attempt to exploit this vulnerability.
   • Use security tools to audit files and certificates for any irregularities.

Examples

To enforce enhanced verification settings, modify the registry to ensure the system checks for certificate revocations:

reg add "HKLM\SOFTWARE\Policies\Microsoft\SystemCertificates\AuthRoot" /v DisableRootAutoUpdate /t REG_DWORD /d 0 /f

References

• Microsoft Security Bulletin MS13-098
• CVE-2013-3900 Detail

Additional Resources

• Microsoft’s Security Update Guide