GHSA-9XWG-3R6F-JCX2 PyMdown Extensions: Path traversal in the b64 extension lets <img src> read files outside base_path

Summary The b64 extension inlines images referenced by as base64 data URIs. When resolving the src path it joins it onto the configured basepath with os.path.normpath and opens the result directly, with no check that the resolved path stays inside basepath. A src containing ../ sequences, or an...