PYSEC-2026-2424

Summary

The compliance-trestle library's remote fetching cache mechanism (HTTPSFetcher and SFTPFetcher) constructs the local cache file path from the URL path component without sanitizing path traversal sequences (../). When a remote OSCAL profile references a URL with traversal in its path, the HTTP response body is written to a location outside the intended cache directory, enabling arbitrary file write with attacker-controlled content to the filesystem.

Attack chain: Malicious OSCAL profile → HTTPS fetch → cache path traversal → arbitrary file write → RCE (via cron, SSH keys, etc.)

Affected Component

Repository: https://github.com/IBM/compliance-trestle File: trestle/core/remote/cache.py (lines 259-266 for HTTPSFetcher, lines 328-333 for SFTPFetcher) Version: v4.0.2 (latest as of 2026-04-30)

Vulnerable Code

cache.py:259-266 — HTTPSFetcher cache path construction

class HTTPSFetcher(FetcherBase):
    def __init__(self, trestle_root: pathlib.Path, uri: str) -> None:
        # ...
        u = parse.urlparse(self._uri)
        # ...
        if u.hostname is None:
            raise TrestleError(f'Cache request for {self._uri} requires hostname')
        https_cached_dir = self._trestle_cache_path / u.hostname
        # ❌ path_parent preserves ../ sequences from URL
        path_parent = pathlib.Path(u.path[re.search('[^/\\\\]', u.path).span()[0] :]).parent
        https_cached_dir = https_cached_dir / path_parent
        https_cached_dir.mkdir(parents=True, exist_ok=True)  # ❌ Creates dirs outside cache
        self._cached_object_path = https_cached_dir / pathlib.Path(pathlib.Path(u.path).name)

cache.py:285-295 — Content written to traversed path

    def _do_fetch(self) -> None:
        # ...
        response = requests.get(self._url, auth=auth, verify=verify, timeout=30)
        if response.status_code == 200:
            result = response.text  # ❌ Attacker-controlled content...