Path Traversal In Chroma.Add_images() Via Unsanitized URI Allows Arbitrary File Read

The encode_image() method in langchain_chroma vectorstores uses Path(uri).open('rb') directly on user-supplied input. No check ensures the resolved path stays within an intended directory, enabling classic path traversal via sequences like ../../../../etc/passwd.

1. Install langchain-chroma and chromadb. 2. Create a Chroma store with embedding_function=None. 3. Call store.add_images(uris=['../../../../etc/passwd']). 4. Observe that the method reads the file and returns base64-encoded content without raising a ValueError.

This hotfix restricts image paths to the current working directory, which may break legitimate applications that pass absolute paths outside cwd. Consider adding a configurable base_dir parameter to add_images() and encode_image(). There is a TOCTOU race between validation and file opening; an attacker with filesystem write access could swap a symlink. Multi-threaded os.chdir() operations could change the meaning of 'cwd' during validation. Rollback: revert encode_image to its original form to restore previous behavior.