Question

I know the < and > characters will cause this error, but what other characters/inputs will cause this error?

I’m testing for this error in the Global.asax, and reridrecting to an error page where I want to list all possible values which cause this error, so the user can go back to their page and get rid of them.

I’ve done some googling, but all I see so far are the < and > characters…surely there are more out there.

Answer 1

 ASP.NET helps protect against script exploits that are disguised as URLs by
 checking for potentially dangerous strings, such as "<!", "</", and "<?".

http://msdn.microsoft.com/en-us/library/w1sw53ds.aspx

from: http://msdn.microsoft.com/en-us/library/system.web.httprequestvalidationexception.aspx

Update: This answer was based on .net 4.0.; for updated tags see https://stackoverflow.com/a/25405146/14753