A penetration tester modifies a web application’s URL by inserting malformed data into input parameters.

The returned error indicates that the application is processing user-controlled input dynamically and failing to handle malformed input properly. A NumberFormatException typically occurs when the application expects a numeric value but receives a string or unexpected format. The error also leaks internal implementation details, including exception type and server-side file path information. The most appropriate next action is dynamic application security testing, because the tester is interacting with the running application, manipulating parameters, observing responses, and identifying weaknesses in input validation, error handling, and information disclosure. This is not evidence of log tampering, since the tester is not modifying or deleting logs. It also does not indicate a memory corruption condition; managed exceptions such as number-format parsing errors are usually logic or validation issues rather than remote buffer overflows. SQL injection is possible in many parameterized web contexts, but this specific error points more directly to improper type handling and verbose error disclosure. This maps to study-guide topics covering DAST, web application testing, input validation, fuzzing, error handling, and secure coding weaknesses.