GitHub Security Advisory: GHSA-7w47-3wg8-547c
Package: gix-index (RUST)
Severity: HIGH (CVSS 8.8)
CWE: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), CWE-23: Relative Path Traversal
Vulnerable versions: < 0.33.0
Patched in: 0.33.0

Summary: gix traversal outside working tree enables arbitrary code execution

Details:
### Summary

During checkout, gitoxide does not verify that paths point to locations in the working tree. A specially crafted repository can, when cloned, place new files anywhere writable by the application.

### Details

Although `gix-worktree-state` checks for collisions with existing files, it does not itself check if a path is really in the working tree when performing a checkout, nor do the path checks in `gix-fs` and `gix-worktree` prevent this. Cloning an untrusted repository containing specially crafted tree or blob names will create new files outside the repository, or inside the repository or a submodule's `.git` directory. The simplest cases are:

- A tree named `..` to traverse upward. This facilitates arbitrary code execution because files can be placed in one or more locations where they are likely to be executed soon.
- A tree named `.git` to enter a `.git` directory. This facilitates arbitrary code execution because hooks can be installed.

A number of alternatives that achieve the same effect are also possible, some of which correspond to specific vulnerabilities that have affected Git in the past:

- A tree or blob whose name contains one or more `/`, to traverse upward or downward. For example, even without containing any tree named `..` or `.git`, a repository can represent a file named `../outside` or `.git/hooks/pre-commit`. This is distinct from the more intuitive case a repository containing trees that represent those paths.
- In Windows, a tree or blob whose name contains one or more `\`, to traverse upward or downward. (Unlike `/`, these are valid on other systems.) See [GHSA-xjx4-8694-q2fq](https://github.com/git/git/security/advisories/GHSA-xjx4-8694-q2fq).
- On a case-insensitive filesystem (such as NTFS, APFS, or HFS+), a tree named as a case variant of `.git`.
- On HFS+, a tree named like `.git` or a case variant, with characters added that HFS+ ignores [in collation](https://developer.apple.com/library/archive/technotes/tn/tn1150.html#StringComparisonAlgorithm). See https://github.com/git/git/commit/6162a1d323d24fd8cbbb1a6145a91fb849b2568f.
- On NTFS, a tree equivalent to `.git` (or a case variant) by the use of [NTFS stream](https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/c54dec26-1551-4d3a-a0ea-4fa40f848eb3) notation, such as `.git::$INDEX_ALLOCATION`. See [GHSA-5wph-8frv-58vj](https://github.com/git/git/security/advisories/GHSA-5wph-8frv-58vj).
- On an NTFS volume with [8.3 aliasing](https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#short-vs-long-names) enabled, a tree named as `git~1` (or a case variant). See [GHSA-589j-mmg9-733v](https://github.com/git/git/security/advisories/GHSA-589j-mmg9-733v).

When a checkout creates some files outside the repository directory but fails to complete, the repository directory is usually removed, but the outside files remain.

### PoC

For simplicity, these examples stage a stand-in file with a valid name, modify the index, and commi