CVE-2015-5209: Special top object can be used to access Struts' internals

The vulnerability stems from improper input validation of request parameters accessing the 'top' object in ValueStack. The primary vulnerable function is ParametersInterceptor.intercept() which handles parameter validation using regex patterns. The security patch modified the exclusion regex to block 'top' references, indicating this was the injection point. HttpParameters.create() is included as a secondary candidate due to its role in parameter processing, though with lower confidence as specific patch details are unavailable. Both functions would appear in stack traces during parameter processing of malicious requests attempting to exploit the 'top' object access.