There are several ways you can protect yourself against a possible ASP.NET Vulnerability:
Use UrlScan to block suspicious URLs before they even reach ASP.NET.
Follow the steps in this KB article (887459) to put code in your Global.asax files to block potentially dangerous URLs.
Add an HttpModule to your web.config or machine.config file that accomplishes the same thing in the KB article.
The nice thing about the first and third options is you can cover an entire server with one step. If you don't have control over the server, you can protect your individual ASP.NET application using the second option.