Critical ASP.NET ViewState Code Injection Vulnerability: What You Need to Know

In February 2025, Microsoft Threat Intelligence revealed a critical security vulnerability affecting ASP.NET applications. The issue stems from developers incorporating publicly available machine keys into their applications, leading to potential remote code execution attacks. Here’s what security teams need to know about this threat and how to protect their systems.

 The Vulnerability Explained

ASP.NET Web Forms use ViewState to preserve page and control state between postbacks. This system relies on two critical machine keys:

• ValidationKey: Creates a message authentication code (MAC) for the ViewState
• DecryptionKey: Handles ViewState encryption

The problem arises when developers use machine keys found in public code repositories or documentation instead of generating unique keys for their applications. Microsoft has identified over 3,000 publicly disclosed keys that could be exploited in what are known as ViewState code injection attacks.

 How the Attack Works

1. Attackers identify systems using known public machine keys
2. They craft malicious ViewState data using these keys
3. The payload is sent to the target website via POST request
4. The ASP.NET Runtime processes the ViewState, validating it successfully due to matching keys
5. Malicious code is loaded into the worker process memory and executed
6. Attackers gain remote code execution capabilities on the IIS web server

(Attack Chain from Microsoft Security)

In December 2024, Microsoft observed attackers using this technique to deliver the Godzilla post-exploitation framework, which enables malicious command execution and shellcode injection.

 Impact and Risks

The use of publicly disclosed keys poses a higher risk than traditional ViewState attacks that rely on stolen keys from dark web forums because:

• The keys are readily available in multiple code repositories
• They may have been incorporated into development code without modification
• Affected servers are vulnerable to remote code execution
• Post-exploitation frameworks can establish persistent backdoors

 Mitigation Steps

Immediate Actions

1. Review your ASP.NET applications for hardcoded machine keys
2. Check machine keys against Microsoft’s published list of compromised keys
3. Remove or rotate any identified public keys
4. Monitor configuration files for unauthorized changes

Long-term Security Measures

1. Securely generate unique machine keys for each application
2. Encrypt sensitive configuration elements including machineKey and connectionStrings
3. Upgrade applications to ASP.NET 4.8 to enable AMSI capabilities
4. Implement attack surface reduction rules on Windows Servers
5. Use Microsoft Defender for Endpoint to detect publicly disclosed keys

For Compromised Systems

If public keys have been exploited:

• Rotating keys alone is insufficient
• Conduct a full investigation of web-facing servers
• Consider complete system reformatting and reinstallation
• Perform offline media restoration where necessary

 How CinchOps Can Help

CinchOps provides several crucial services to protect against ViewState code injection attacks:

1. Configuration Monitoring: Real-time monitoring of web.config and other critical configuration files, with immediate alerts for unauthorized changes.
2. Security Scanning: Regular automated scans to detect the presence of known vulnerable machine keys in your applications.
3. Deployment Protection: Built-in safeguards prevent the deployment of applications using known public machine keys.
4. Incident Response: If compromised keys are detected, our platform can automatically initiate containment procedures and guide recovery efforts.

By implementing these protective measures through CinchOps, organizations can significantly reduce their risk exposure to ViewState code injection attacks while maintaining operational efficiency.

Remember: Security is a continuous process, not a one-time fix. Regular audits and updates remain essential for maintaining a strong security posture.

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