The vulnerability stems from improper path handling when processing URL paths. The advisory explicitly mentions directory traversal via appended slashes, which typically occurs when user-supplied paths are joined with a base directory without proper sanitization. In Node.js static servers, this logic is commonly found in the core request-serving function (often named 'serve'). The function would use path.join() or similar methods without subsequent validation to ensure the resolved path remains within the intended directory. This matches the CWE-22 pattern and the described attack vector.