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Complete Input Handling and Parser Attacks, or equivalent HTTP and Linux fundamentals, before this module. In this module of the Web CTF learning path, you move from parser trust failures into upload and command execution filter logic. You override a client declared multipart type to bypass an upload gate that never inspects actual file content, and you map a command injection filter's own logic closely enough to find the narrow exception path it leaves open. Legacy PHP running on an older Debian base backs every challenge in this lab. Treat that runtime as compatibility debt, not as a modern framework default, and note where a current stack would already close these gaps. Upon completion of the module, students will be able to: • Identify an upload filter that trusts a client declared Content-Type instead of inspecting actual file content. • Override a multipart Content-Type field independently of a file's real content to bypass a weak upload gate. • Read a command injection filter's logic precisely enough to distinguish what it blocks from what it unintentionally allows. • Explain why a filtered exception path is still command injection, scoped correctly rather than reported as unrestricted remote code execution. For inquiries, please write us at https://www.darkrelay.com/cybersecurity-course-inquiry