Request Validation (aka the ValidateRequest filters) in ASP.NET in Microsoft .NET Framework without the MS07-040 update does not properly detect dangerous client input, which allows remote attackers to conduct cross-site scripting (XSS) attacks, as demonstrated by a query string containing a "</" (less-than slash) sequence.
https://exchange.xforce.ibmcloud.com/vulnerabilities/44741
http://www.securityfocus.com/archive/1/495667/100/0/threaded