Rule Definition
By directly using content of Request variables, you expose your application to data injection (SQL-Injection and so forth).

Remediation
Always use a validation function that check the data input (for example that the data does not contain ' etc). Assign this value to a variable (preferably using a naming convention to distinguish safe from unsafe data), and then always use that variable.

Violation Code Sample

String unsafe = Request.Form["UserData"];
..
.. // use unsafe

=> This is unsafe to use that value directly. For example if this variable is used in a SQL-Query, it is very easy to do some SQL-Injection.

Fixed Code Sample

String safe=MyFilterStringFunction(Request.Form["UserData"]);

=> By processing the entry in the MyFilterStringFunction you can ensure that the data will not lead to SQL-Injection or other kind of attack.
Use name convention for the variable containing the safe data to distinguish it. Always use that variable afterwards.

Hacking the Code: ASP.NET Web Application Security by Mark M. Burnett and James C. Foster ISBN:1932266658 Syngress Publishing (c) 2004