Open redirect vulnerability in the Forms Authentication feature in the ASP.NET subsystem in Microsoft .NET Framework 2.0 SP2, 3.5 SP1, 3.5.1, and 4.0 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a crafted return URL, aka "Insecure Redirect in .NET Form Authentication Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A14815
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2011/ms11-100
http://www.securityfocus.com/bid/51202