It is easy for developers to forget to update validation logic when they make changes to an ActionForm class. One indication that validation logic is not being properly maintained is inconsistencies between the action form and the validation form.
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.