Associated Vulnerability
Title:WinVerifyTrust Signature Validation Vulnerability (CVE-2013-3900)Description:Why is Microsoft republishing a CVE from 2013? We are republishing CVE-2013-3900 in the Security Update Guide to update the Security Updates table and to inform customers that the EnableCertPaddingCheck is available in all currently supported versions of Windows 10 and Windows 11. While the format is different from the original CVE published in 2013, except for clarifications about how to configure the EnableCertPaddingCheck registry value, the information herein remains unchanged from the original text published on December 10, 2013, Microsoft does not plan to enforce the stricter verification behavior as a default functionality on supported releases of Microsoft Windows. This behavior remains available as an opt-in feature via reg key setting, and is available on supported editions of Windows released since December 10, 2013. This includes all currently supported versions of Windows 10 and Windows 11. The supporting code for this reg key was incorporated at the time of release for Windows 10 and Windows 11, so no security update is required; however, the reg key must be set. See the Security Updates table for the list of affected software. Vulnerability Description A remote code execution vulnerability exists in the way that the WinVerifyTrust function handles Windows Authenticode signature verification for portable executable (PE) files. An anonymous attacker could exploit the vulnerability by modifying an existing signed executable file to leverage unverified portions of the file in such a way as to add malicious code to the file without invalidating the signature. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. Exploitation of this vulnerability requires that a user or application run or install a specially crafted, signed PE file. An attacker could modify an... See more at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2013-3900
Readme
# Remediation Report: CVE-2013-3900 – WinVerifyTrust Vulnerability on Windows Server 2019 (Azure VM)
---
## Overview
During a recent authenticated vulnerability assessment conducted using Tenable Nessus, **[CVE-2013-3900](https://www.cve.org/CVERecord?id=CVE-2013-3900)** was detected on a **Windows Server 2019** virtual machine hosted in **Microsoft Azure**. This scan leveraged administrative credentials, allowing for in-depth inspection of the system’s configuration and registry settings.
The issue stems from a flaw in how Windows handles signature validation via the `WinVerifyTrust` function. Exploiting this vulnerability, a malicious actor could bypass integrity checks by appending data to signed executable files—potentially leading to the execution of untrusted code under the guise of a valid signature. (Source: [Microsoft](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2013-3900))
---
## Vulnerability Details
- **CVE**: [CVE-2013-3900](https://www.cve.org/CVERecord?id=CVE-2013-3900)
- **Severity**: High
- **Affected Component**: WinVerifyTrust Signature Validation
- **Risk**: Digital signature bypass through improper handling of certificate padding
---
## Remediation Plan
To address this issue, Microsoft recommends enabling the `EnableCertPaddingCheck` registry setting. This enforces stricter validation and prevents the acceptance of improperly padded PE files.
---
## Mitigation Procedure
### Step 1: Launch Command Prompt with Elevated Privileges
- Open Start Menu
- Search for `cmd`, right-click, and select **Run as Administrator**
### Step 2: Execute Registry Fix
Use the following commands to modify registry values for both 64-bit and 32-bit subsystems:
```cmd
reg add "HKLM\Software\Microsoft\Cryptography\Wintrust\Config" /v EnableCertPaddingCheck /t REG_DWORD /d 1 /f
reg add "HKLM\Software\Wow6432Node\Microsoft\Cryptography\Wintrust\Config" /v EnableCertPaddingCheck /t REG_DWORD /d 1 /f
```
### Step 3: Restart the Virtual Machine
Once the registry keys were successfully added, a **system reboot** was performed to ensure the configuration changes took full effect across all active services and processes.
---
## Post-Remediation Verification
A follow-up **credentialed Nessus scan** was conducted after the reboot. The vulnerability **CVE-2013-3900 no longer appeared** in the scan results, confirming that the mitigation steps were successful and the system is no longer vulnerable to this signature bypass exploit.
---
## Why This Matters: Risks of Not Remediating CVE-2013-3900
Leaving this vulnerability unaddressed could lead to several significant security and compliance risks:
- **Bypassing Digital Signature Verification**
Attackers may embed malicious code in signed executables without invalidating the signature.
- **Avoidance of Security Tools**
Malware can evade antivirus, endpoint detection and response (EDR), and application whitelisting mechanisms.
- **Privilege Escalation & Remote Code Execution**
Exploitation may lead to system compromise, data exfiltration, or lateral movement within the network.
- **Software Supply Chain Attacks**
Unsuspecting users may install tampered software that appears to be signed and trusted.
- **Regulatory & Legal Exposure**
Non-remediation may violate security requirements under **HIPAA**, **NIST**, **PCI-DSS**, **CMMC**, and other frameworks.
---
## Conclusion
**CVE-2013-3900** presents a serious threat by undermining trust in signed software. Through prompt detection, registry-level remediation, and verification via credentialed scanning, this vulnerability was successfully mitigated on the affected Windows Server 2019 system.
This process reinforces the importance of:
- Regular vulnerability scans using authenticated credentials
- Prompt application of vendor-recommended configurations
- Continuous monitoring and validation of mitigation efforts
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