serve_cache_file gated the resolved path with file_path.startswith(os.path.abspath(CACHE_DIR)) without a trailing os.sep, so any path resolving to a sibling whose name starts with the cache-dir basename (e.g. cache_backup, cached_models) passed the prefix check. Authenticated users could read files from such siblings via /cache/../<sibling>/<file>. Appending os.sep to the prefix closes the bypass; deep traversal and absolute paths were already correctly blocked.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
