Windows - Security - Mitigate WinVerifyTrust Signature Validation (CVE-2013-3900)

What the CVE-2013-3900 signature validation remediation does

This Automox Worklet™ mitigates CVE-2013-3900 by configuring Windows Authenticode signature verification to detect and reject modified signed executables. The Worklet sets the EnableCertPaddingCheck registry value to 1 in both the 32-bit and 64-bit registry hives to enable Microsoft's recommended certificate padding validation.

CVE-2013-3900 is a critical remote code execution flaw that allows attackers to modify legitimate signed portable executable (PE) files–such as .exe, .sys, and .dll files–by adding malicious code without invalidating the digital signature. This means Windows systems could execute compromised code while still trusting the file as legitimate.

The Worklet configures two registry paths that handle 32-bit and 64-bit application compatibility. By enabling certificate padding checks, the Worklet prevents Windows from accepting signed files that have been tampered with after signing, closing the attack vector that enabled distribution of signed malware and ransomware.

Why disable Authenticode signature padding exploitation

Attackers have exploited CVE-2013-3900 for over a decade to distribute signed malware, ransomware, and advanced persistent threat (APT) tools. The vulnerability received inclusion in CISA's Known Exploited Vulnerabilities Catalog because adversaries actively weaponize it. Microsoft updated its guidance in January 2022, shifting responsibility to organizations to configure non-default protection on all Windows systems.

Your endpoints face elevated risk from supply chain compromises and targeted attacks when padding validation is disabled. Enabling certificate padding checks costs zero performance impact while eliminating a primary attack vector for malware distribution that criminals continue to abuse in the wild.

Compliance frameworks including CIS Benchmarks reference this control. Organizations in regulated industries benefit from documented evidence that they have remediated known exploited vulnerabilities. The fix requires no endpoint restart and does not impact legitimate software execution.

How certificate padding validation enforcement works

1. Evaluation phase: The Worklet checks the EnableCertPaddingCheck registry value in two locations: HKLM:\SOFTWARE\Microsoft\Cryptography\Wintrust\Config (32-bit path) and HKLM:\SOFTWARE\Wow6432Node\Microsoft\Cryptography\Wintrust\Config (64-bit compatibility path). The Worklet verifies both values are set to 1 (string type) in their respective registry hives. If either registry path is missing or the value is not set to 1, the endpoint is flagged for remediation. If both registry entries are correctly configured, the endpoint is marked compliant and the Worklet exits without remediation.

2. Remediation phase: The Worklet creates or updates the EnableCertPaddingCheck registry value in the 32-bit configuration path (HKLM:\SOFTWARE\Microsoft\Cryptography\Wintrust\Config) and the 64-bit compatibility path (HKLM:\SOFTWARE\Wow6432Node\Microsoft\Cryptography\Wintrust\Config) to 1. Both values are set as REG_SZ (string) type. If the registry key does not exist, the Worklet creates it automatically. The change takes effect immediately without requiring a restart. The Worklet logs successful configuration of each registry entry.

CVE-2013-3900 remediation requirements

• Windows 10, Windows 11, Windows Server 2016 or later versions

• PowerShell 3.0 or higher (PowerShell 5.0 and higher recommended)

• Local Administrator privileges to modify HKEY_LOCAL_MACHINE registry hives

• No pending system restarts or software installations in progress

• Windows Cryptography Services running normally (the Worklet does not interrupt this service)

Expected Authenticode signature validation enforcement

After successful remediation, Windows will enforce certificate padding validation whenever checking the digital signature of executable files. The operating system will reject any signed PE files that show signs of modification after signing, preventing the execution of malware that exploits this vulnerability.

Legitimate software continues to execute normally because genuine signed code has not been modified. The change introduces zero performance overhead and requires no additional user action. Your endpoints gain protection against signed malware distribution without impacting daily operations. You can verify successful remediation by checking that the EnableCertPaddingCheck registry values equal 1 in both 32-bit and 64-bit paths.