Microsoft Threat Intelligence observed limited activity by an unattributed threat actor using a publicly available, static ASP.NET machine key to inject malicious code and deliver the Godzilla post-exploitation framework. In the course of investigating, remediating, and building protections against this activity, we observed an insecure practice whereby developers have incorporated various publicly disclosed ASP.NET machine keys from publicly accessible resources, such as code documentation and repositories, which threat actors have used to launch ViewState code injection attacks and perform malicious actions on target servers.

In modern web development, while cookies are the go-to method for transmitting session IDs, the .NET Framework also provides an alternative: encoding the session ID directly in the URL. This method is useful to clients that do not support cookies.