GitPython versions before 3.1.52 contain a vulnerability in Repo.clone_from() that allows environment variable exfiltration. The function passes caller-supplied remote URLs through Git.polish_url(), which calls os.path.expandvars() on non-Cygwin platforms before invoking git clone. An attacker who controls the clone URL can embed shell variable tokens such as $NAME or ${NAME} that get expanded to actual environment variable values in the hosting process. Sensitive credentials such as AWS_SECRET_ACCESS_KEY or GITHUB_TOKEN can be embedded into the resulting URL. This expanded URL is then transmitted over the network to an attacker-controlled host during the clone attempt, effectively disclosing the secret. The fix is to upgrade to GitPython 3.1.52 or later.