Request Validation (aka the ValidateRequest filters) in ASP.NET in Microsoft .NET Framework with 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 tilde slash) sequence followed by a crafted STYLE element.
https://exchange.xforce.ibmcloud.com/vulnerabilities/44743
http://www.securityfocus.com/archive/1/496071/100/0/threaded
http://www.securityfocus.com/archive/1/495667/100/0/threaded
http://www.procheckup.com/Vulnerability_PR08-20.php
http://www.procheckup.com/PDFs/bypassing-dot-NET-ValidateRequest.pdf