gix and gitoxide's symlinked .gitmodules are followed and parsed from outside of the repository

Overview

Summary

attachments: pocs.zip

When Repository::submodules() loads submodule metadata, it prefers the worktree .gitmodules file if that path exists. In the current implementation, the path is read with std::fs::read(), which follows symlinks. As a result, a repository can present a symlinked .gitmodules that points outside the repository, and gitoxide will parse the out-of-repository bytes as submodule configuration.

This is a repository-boundary violation. A caller using the high-level submodule API can believe it is reading repository-local submodule metadata, while the bytes are actually coming from an arbitrary file outside the repository tree.

Root cause analysis

The relevant flow is:

1. gix/src/repository/location.rs derives the worktree .gitmodules path as workdir/.gitmodules.
2. gix/src/repository/submodule.rs reads that path with std::fs::read(&path) and immediately parses the bytes as a submodule configuration file.
3. Repository::submodules() exposes the parsed entries through the high-level API.

The issue is not in the parser. The issue is that the worktree path is treated as an ordinary file without checking whether it is a symlink, and without checking whether the canonicalized target remains inside the repository worktree.

Because std::fs::read() follows symlinks, a malicious repository can cause gitoxide to ingest bytes from an attacker-chosen location outside the repository. The resulting Submodule objects then expose name, path, and url values derived from that external file.

Reproduction steps

Use the attached PoC zip that contains the pocs/ workspace.

1. Unzip the PoC archive.

2. Enter pocs/F001.

3. Run:

   cargo run --quiet
   

4. Compare the output with pocs/F001/result.txt.

Important outputs include:

• gitmodules_symlink=.../victim-repo/.gitmodules
• symlink_target=.../outside/modules.conf
• parsed_name=symlinked
• parsed_path=deps/symlinked
• parsed_url=https://attacker.example/symlinked.git

These outputs show that gitoxide parsed the submodule configuration from the symlink target outside the repository, not from repository-local bytes.

Impact

Confirmed impact:

• out-of-repository bytes can be injected into the result of Repository::submodules();
• callers can be misled about submodule metadata such as name, path, and url;
• any downstream workflow that uses those values to decide clone, fetch, update, or policy behavior is operating on attacker-controlled data that did not actually originate from the repository tree.

This report does not claim direct command execution from this code path by itself. The demonstrated impact is metadata injection across the repository boundary.

Recommended fix

A safe fix is to stop silently following symlinks for the worktree .gitmodules path in this loading path.

Reasonable options include:

1. use symlink_metadata() / lstatstyle checks and reject symlinked .gitmodules when loading from the worktree;
2. canonicalize the target and verify that it still resides under the repository worktree before reading it;
3. for security-sensitive callers, prefer loading .gitmodules from the index or HEAD tree rather than following the worktree path.

At minimum, the worktree path should not silently follow symlinks to arbitrary external files.

Affected packages

• gitoxide < 0.52.1
• gix < 0.83.0

Remediation

Upgrade to a patched release:

• gitoxide 0.52.1
• gix 0.83.0