GitPython submodule update path traversal can write outside the repository

Affected: GitPython 3.1.61 (latest release) and main — git/objects/submodule/base.py. git diff 3.1.61 origin/main -- git/objects/submodule/ is empty, so both are identical here.

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The gap

The fix for GHSA-hmq2-w58f-27jc added Submodule._validated_name() and wired it into update() and five siblings, closing the .gitmodules name → .git/modules/<name> traversal. The other attacker-controlled .gitmodules field, path, is read raw:

# git/objects/submodule/base.py:172-177
def _set_cache_(self, attr):
    if attr in ("path", "_url", "_branch_path"):
        reader = self.config_reader()
        self.path = reader.get("path")          # raw .gitmodules value

and GitPython's own containment guard is applied in only two of the places that consume it:

400: def _to_relative_path(cls, parent_repo, path)      # the guard (abspath + commonpath containment)
542:     path = cls._to_relative_path(repo, path)        # add()   — guarded
1041:    module_checkout_path = self._to_relative_path(self.repo, module_path)   # move() — guarded

update() validates only the name and then uses the path-derived absolute location directly:

788:  self._validated_name(self.name)                    # NAME only
801:  checkout_module_abspath = self.abspath             # derived from self.path — unguarded
821:  os.makedirs(checkout_module_abspath, exist_ok=True)

So path = ../../../tmp/escaped in an attacker-authored .gitmodules selects the directory that gets created and, on the clone path, populated from the submodule URL. The same absolute location is what force_remove hands to shutil.rmtree.

The asymmetry is the argument: this is not a missing concept — the project wrote _to_relative_path() precisely for this, and add()/move() use it. update() does not.

Honest limits (please read before rating)

• The most common flow is not affected. Repo.clone_from(...) → repo.submodules → sm.update(init=True) re-derives path from a canonical tree lookup, and real git refuses to check out a tree containing a .. component, so an evil .gitmodules never lands in the working tree in the first place. A reachable trigger therefore requires the victim's code to name a non-HEAD commit (a historical-commit API such as submodule_update(previous_commit=...)).
• The researcher did not build that end-to-end trigger. The researcher only verified first-hand the code above: the guard's two call sites, the name-only validation in update(), and the unguarded abspath → os.makedirs() flow at 3.1.61 == main.

Suggested fix

Apply the guard the project already has, wherever the path is consumed:

# in update(), before deriving abspath (and in any other consumer of self.path):
checkout_rel = self._to_relative_path(self.repo, self.path)   # raises if it escapes the working tree

Better still, validate at the boundary: reject a .gitmodules entry whose path is absolute or contains a .. component when the section is first read in _set_cache_()/iter_items(), so no consumer can be added later without the check. A regression test with path = ../escaped alongside the existing name test would pin both fields.

Prior art checked

GHSA-hmq2-w58f-27jc (this is a residual of its fix, in the sibling field, not a re-report) plus the repository's 30 published advisories — none mentions the path field or _to_relative_path. Searched issues and PRs for _to_relative_path, gitmodules path and submodule traversal: no report of this.

Credit

kta1kri.

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Appendix — EVIDENCE_gitpython_path_unguarded_20260901.txt (inlined; advisories accept no attachments)

=== EVIDENCE: GitPython — the .gitmodules 'path' field reaches os.makedirs()/clone unguarded ===
Mon Aug 31 18:45:22 UTC 2026

--- artifact: tag 3.1.61 (latest release); git diff 3.1.61 origin/main -- git/objects/submodule/ is empty ---

--- the containment guard GitPython owns, and its only two call sites ---
33:    _to_relative_path,
400:    def _to_relative_path(cls, parent_repo: "Repo", path: PathLike) -> PathLike:
407:            path = _to_relative_path(parent_repo.working_tree_dir, path)
542:        path = cls._to_relative_path(repo, path)
1041:        module_checkout_path = self._to_relative_path(self.repo, module_path)

--- the parent fix (_validated_name) call sites: it validates the NAME ---
309:    def _validated_name(cls, name: str) -> str:
321:        name = cls._validated_name(name)
541:        cls._validated_name(name)
788:            self._validated_name(self.name)
1040:        self._validated_name(self.name)
1181:        self._validated_name(self.name)
1439:        self._validated_name(self.name)
1440:        self._validated_name(new_name)
1489:        self._validated_name(self.name)

--- update(): name validated, path not; abspath -> os.makedirs ---

        try:
            self._validated_name(self.name)

            # ENSURE REPO IS PRESENT AND UP-TO-DATE
                # END early abort if init is not allowed

                checkout_module_abspath = self.abspath
                module_abspath = self._module_abspath(self.repo, self.path, self.name)

                # ``git submodule deinit`` leaves the repository in
                # ``.git/modules`` and empties the checkout. Reconnect that retained
                # repository instead of trying to clone over it.
                if not dry_run and osp.isdir(module_abspath):
                    try:
                        git.Repo(module_abspath)
                    except InvalidGitRepositoryError:
                        pass
                    else:
                        if osp.lexists(checkout_module_abspath) and (
                            osp.islink(checkout_module_abspath)
                            or not osp.isdir(checkout_module_abspath)
                            or os.listdir(checkout_module_abspath)
                        ):
                            raise OSError(
                                "Module directory at %r does already exist and is non-empty" % checkout_module_abspath
                            )
                        os.makedirs(checkout_module_abspath, exist_ok=True)
                        self._write_git_file_and_module_config(checkout_module_abspath, module_abspath)
                        mrepo = git.Repo(checkout_module_abspath)

--- where self.path comes from (raw .gitmodules value) ---
    def _set_cache_(self, attr: str) -> None:
        if attr in ("path", "_url", "_branch_path"):
            reader: SectionConstraint = self.config_reader()
            # Default submodule values.
            try:
                self.path = reader.get("path")
            except cp.NoSectionError as e: