Microsoft .NET Framework 1.1 SP1, 2.0 SP1 and SP2, 3.5, 3.5 SP1, 3.5.1, and 4.0, as used for ASP.NET in Microsoft Internet Information Services (IIS), provides detailed error codes during decryption attempts, which allows remote attackers to decrypt and modify encrypted View State (aka __VIEWSTATE) form data, and possibly forge cookies or read application files, via a padding oracle attack, aka "ASP.NET Padding Oracle Vulnerability."
The Common Language Runtime (CLR) in Microsoft .NET Framework 2.0 SP1, 2.0 SP2, 3.5, 3.5 SP1, and 3.5.1, and Microsoft Silverlight 2 and 3 before 3.0.50611.0 on Windows and before 3.0.41130.0 on Mac OS X, does not properly handle interfaces and delegations to virtual methods, which allows remote attackers to execute arbitrary code via (1) a crafted XAML browser application (aka XBAP), (2) a crafted ASP.NET application, or (3) a crafted .NET Framework application, aka "Microsoft Silverlight and Microsoft .NET Framework CLR Virtual Method Delegate Vulnerability."