GHSA-rwj8-pgh3-r573: GitPython: Environment-variable exfiltration via os.path.expandvars() on Repo.clone_from() URL

Summary Repo.clone_from() passes the caller-supplied remote URL through Git.polish_url(), which on every non-Cygwin platform calls os.path.expandvars() on the URL before handing it to git clone. An attacker who controls the URL argument — the documented use case for clone_from() in "import repository from URL" features of CI servers, git-hosting mirrors, and dependency scanners — can embed $NAME / ${NAME} tokens that are expanded server-side to the values of the hosting process's environment variables. The resulting URL, now containing the secret, is transmitted over the network to the attacker-named host. This crosses the trust boundary between an untrusted remote URL and the server's process environment, disclosing secrets such as AWS_SECRET_ACCESS_KEY or GITHUB_TOKEN with no precondition beyond the ability to submit a clone URL. Details Affected versions: gitpython (PyPI) — all releases up to and including 3.1.50 (latest at time of reporting); confirmed present on the main branch. Git.polish_url() unconditionally applies environment-variable expansion to its input on the non-Cygwin branch: git/cmd.py (v3.1.50), lines 907–925: @classmethod def polish_url(cls, url: str, is_cygwin: Union[None, bool] = None) -> PathLike: """Remove any backslashes from URLs to be written in config files. ... """ if is_cygwin is None: is_cygwin = cls.is_cygwin() if is_cygwin: url = cygpath(url) else: url = os.path.expandvars(url) # <-- line 921 if url.startswith("~"): url = os.path.expanduser(url) url = url.replace("\\\\", "\\").replace("\\", "/") return url Repo._clone() — reached from the public Repo.clone_from() (git/repo/base.py:1520) and Repo.clone() — runs the unsafe-protocol check on the raw URL and then passes the polished (post-expansion) URL to the git clone subprocess: git/repo/base.py (v3.1.50), lines 1407–1418: if not allow_unsafe_protocols: Git.check_unsafe_protocols(url) if not allow_unsafe_options: Git.check_unsafe_options(options=list(kwargs.keys()), unsafe_opt