ASP.NET Request Validation

ASP.NET Provides built-in request validation on form submission or postback handling. Request validation is on by default, and is handled differently by versions of the framework.

ASP.NET 1.1 Request Validation Summary

• Filter "&#"
• Filter ‘<’ then alphas or ! or / (tags)
• Filter "script:"
• Filter on handlers (onXXX=)
• Filter “expression(“
• Ignore elements named "__VIEWSTATE"

ASP.NET 2.0 Request Validation Summary

• Filter &#
• Filter ‘<’ then alphas or ! or / (tags)

*Ignore elements with names prefixed with double underscore (__)

To toggle request validation (it is set to true by default):

On a single page:

 <%@ Page validateRequest="true|false" %>

For the entire application:

 <configuration>
    <system.web>
         <pages validateRequest="true|false" />
    </system.web>
 </configuration>

References

Validation - Preventing Script Attacks
ASP.NET 2.0 dumb’s down request validation (by Michael Eddington)