Omitting validation for even a single input field may give attackers the leeway they need to compromise your application. Unchecked input is the root cause of some of today's worst and most common software security problems. Cross-site scripting, SQL injection, and process control vulnerabilities can stem from incomplete or absent input validation. Although J2EE applications are not generally susceptible to memory corruption attacks, if a J2EE application interfaces with native code that does not perform array bounds checking, an attacker may be able to use an input validation mistake in the J2EE application to launch a buffer overflow attack. Some applications use the same ActionForm for more than one purpose. In situations like this, some fields may go unused under some action mappings. It is critical that unused fields be validated too. Preferably, unused fields should be constrained so that they can only be empty or undefined. If unused fields are not validated, shared business logic in an action may allow attackers to bypass the validation checks that are performed for other uses of the form.