The Forms Authentication feature in the ASP.NET subsystem in Microsoft .NET Framework 1.1 SP1, 2.0 SP2, 3.5 SP1, 3.5.1, and 4.0, when sliding expiry is enabled, does not properly handle cached content, which allows remote attackers to obtain access to arbitrary user accounts via a crafted URL, aka "ASP.NET Forms Authentication Ticket Caching Vulnerability."