Microsoft Threat Intelligence has revealed a significant security concern affecting ASP.NET applications worldwide. Cybercriminals are actively exploiting publicly available ASP.NET machine keys to conduct sophisticated ViewState-based attacks, potentially compromising thousands of web servers. This emerging threat vector specifically targets applications using default or publicly sourced validationKey and decryptionKey values.
Understanding the ViewState Attack Vector
The attack leverages ASP.NET Web Forms’ ViewState mechanism, which manages page state persistence between client requests. Threat actors craft malicious ViewState payloads signed with legitimate machine keys harvested from public repositories. These payloads pass server-side validation checks due to matching cryptographic signatures, enabling remote code execution (RCE) capabilities on vulnerable systems.
Scope and Real-World Impact
Microsoft’s investigation has uncovered more than 3,000 exposed ASP.NET machine keys in public code repositories, creating an extensive attack surface. A notable incident in December 2024 demonstrated the severity of this vulnerability when attackers successfully deployed the Godzilla framework using a compromised public key, establishing persistent access to the targeted server through malicious command execution.
Technical Implementation of the Attack
The exploitation process involves several stages: first, attackers identify vulnerable applications using public machine keys. They then generate specially crafted ViewState data, signing it with known keys. When the target server processes this data, it validates the signature as legitimate, allowing the execution of embedded malicious code within the application’s trust boundary.
Security Mitigation Strategies
To protect against ViewState-based attacks, security professionals should implement these critical measures:
– Generate unique, cryptographically secure machine keys for each application deployment
– Implement proper encryption for machineKey and connectionStrings configurations
– Upgrade to ASP.NET 4.8 to leverage enhanced security features including AMSI integration
– Deploy comprehensive Windows Server security controls
– Regularly audit application configurations for exposed machine keys
In response to this threat, Microsoft has taken proactive steps by removing example machine keys from their documentation and providing detailed guidance for key rotation through PowerShell and IIS Management Console. Organizations must conduct immediate security audits to identify and replace potentially compromised machine keys, implementing robust key management practices to prevent future exploitation. The incident serves as a crucial reminder that even seemingly harmless configuration sharing can create significant security vulnerabilities in web applications.
