GHSA-fcv2-xgw5-pqxf
MEDIUMsigstore legacy TUF client allows for arbitrary file writes with target cache path traversal
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/sigstore/sigstoreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
The legacy TUF client pkg/tuf/client.go, which supports caching target files to disk, constructs a filesystem path by joining a cache base directory with a target name sourced from signed target metadata, but it does not validate that the resulting path stays within the cache base directory.
Note that this should only affect clients that are directly using the TUF client in sigstore/sigstore or are using an older version of Cosign. As this TUF client implementation is deprecated, users should migrate to https://github.com/sigstore/sigstore-go/tree/main/pkg/tuf as soon as possible.
Note that this does not affect users of the public Sigstore deployment, where TUF metadata is validated by a quorum of trusted collaborators.
Impact
A malicious TUF repository can trigger arbitrary file overwriting, limited to the permissions that the calling process has.
Workarounds
Users can disable disk caching for the legacy client by setting SIGSTORE_NO_CACHE=true in the environment, migrate to https://github.com/sigstore/sigstore-go/tree/main/pkg/tuf, or upgrade to the latest sigstore/sigstore release.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/sigstore/sigstore | all versions | 1.10.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sigstore/sigstore. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/sigstore/sigstore to 1.10.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fcv2-xgw5-pqxf 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.
How O3 protects you
O3 pinpoints whether GHSA-fcv2-xgw5-pqxf is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-fcv2-xgw5-pqxf. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-fcv2-xgw5-pqxf in your dependencies?
O3 detects GHSA-fcv2-xgw5-pqxf across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.