GHSA-f89h-2fjh-2r9q — gix-fs
HIGHGHSA-f89h-2fjh-2r9q is a high-severity (CVSS 7.8) CWE-59 vulnerability in gix-fs. A fix is available for gix-fs — see the affected versions and patch details below.
gix-fs: Symlink prefix-reuse allows worktree escape during checkout
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for GHSA-f89h-2fjh-2r9q.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-f89h-2fjh-2r9q by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
gix-fsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Summary
A malicious tree can be constructed that will, when checked out with gitoxide, permit writing an attacker-controlled symlink into any existing directory the user has write access to.
Details
During checkout, all symlink index entries are deferred and created after regular files using a single shared gix_worktree::Stack. Internally, this uses a gix_fs::Stack.
gix_fs::Stack::make_relative_path_current() caches validated path prefixes: when the previously-processed leaf component exactly matches the leading component(s) of the next path, the leaf-to-directory transition at gix-fs/src/stack.rs:195-197 invokes only delegate.push_directory(), never delegate.push().
In gix_worktree::stack::delegate::StackDelegate, when the state member is State::CreateDirectoryAndAttributesStack, Attributes::push_directory() only loads attributes (from the ODB, in the clone case), and does not perform any other checks. The on-disk symlink_metadata() check and unlink-on-collision live in StackDelegate::push()'s invocation of create_leading_directory(), which is therefore bypassed for the cached prefix. The final symlink is created with plain std::os::unix::fs::symlink, which follows symlinks in parent directories.
Therefore, it's possible to provide a tree with duplicate symlink and directory entries that exploits this. If a tree is constructed with:
- A
120000(symlink) entryathat points to.git/hooks. - A
040000(directory) entryawith a subtree that contains a symlink frompost-checkoutto../../payload. - A
100755(executable file) entrypayload.
This is converted by gix_index::State::from_tree() into index entries ["a" (SYMLINK), "a/post-checkout" (SYMLINK)].
Then, during the delayed symlink phase:
ais created as a symlink to e.g..git/hooks.- When processing
a/post-checkout, theaprefix is reused from the just-processed leaf entry without re-running the intermediate-directory check, after which… symlink(target, "<wt>/a/post-checkout")resolves through the just-created symlink to write.git/hooks/post-checkout.
Although this example uses .git/hooks for simplicity, there's no actual requirement to write within the repo checkout. This can be fairly easily chained into code execution by writing to something that is known to be executed — for example, by writing to .git/hooks/post-checkout if the attacker knows that a hook-aware Git implementation will be used later, or by writing to something like ~/.local/bin.
PoC
Attached is build-bad-repo.sh, which builds a repo with the aforementioned tree structure. Cloning it with gix will set up the malicious .git/hooks/post-checkout, at which point anything that normally invokes the post-checkout hook will result in its execution, such as git checkout -b new-branch.
Impact
Arbitrary symlink creation into any existing directory the user can write to.
Disclosure
This vulnerability was found by AI (specifically, Claude Mythos) as part of Project Glasswing. This advisory was written and verified by a human.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | gix-fs | all versions | 0.21.1cargo update -p gix-fs --precise 0.21.1 |
Affected Products
gix-fsgitoxidelabsDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for gix-fs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update gix-fs to 0.21.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-f89h-2fjh-2r9q is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is GHSA-f89h-2fjh-2r9q in your dependencies?
Find it across crates.io, including transitive dependencies.