Your applications will run faster, your security team will sleep better, and attackers will move on to easier targets.
This is a cryptographic weakness in the way .NET 4.0 implemented the view state validation and forms authentication. An attacker could decrypt, tamper with, and re-encrypt authentication cookies. microsoft net framework 4.0 v 30319 vulnerabilities
Flaws in how the framework manages memory or web requests can lead to the leaking of sensitive data, such as cryptographic keys or user credentials, to unauthorized parties. Your applications will run faster, your security team
Several vulnerabilities have been identified in Microsoft .NET Framework 4.0 v3.03019, including: Your applications will run faster