X-aspnet-version 4.0.3 Vulnerabilities ^hot^ -

While this header was originally intended for debugging and compatibility purposes, in the hands of a malicious actor, it serves as a reconnaissance tool. It tells the attacker exactly which weapon to select from their arsenal.

A common point of confusion is the version number 4.0.30319 . This actually refers to the version, rather than the specific .NET Framework version (like 4.7.2 or 4.8). Because all versions of .NET Framework from 4.0 through 4.8.x share this same CLR version, the header itself doesn't tell an attacker exactly which patches you have applied, but it does confirm you are running on an older, non-Core version of the framework. Key Vulnerabilities Associated with CLR 4.0.30319 x-aspnet-version 4.0.3 vulnerabilities

X-AspNet-Version: 4.0.30319 HTTP response header indicates that an application is running on the .NET Common Language Runtime (CLR) 4.0 While this header was originally intended for debugging

If the header is present and the app uses vulnerable ViewState configuration: This actually refers to the version, rather than

Consider a real-world scenario: