GHSA-5fhj-g3p3-pq9g is a medium-severity (CVSS 6.4) Use After Free vulnerability in wasmtime. O3 Security confirms whether GHSA-5fhj-g3p3-pq9g is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Wasmtime vulnerable to Use After Free with `externref`s
Real-World Exposure
wasmtime🦀cranelift-codegenReal-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
There is a bug in Wasmtime's code generator, Cranelift, where functions using reference types may be incorrectly missing metadata required for runtime garbage collection (GC). This means that if a GC happens at runtime then the collector will mistakenly think some Wasm stack frames do not have live references to garbage collected values and therefore reclaim and deallocate them. The function can then subsequently continue to use the values, leading later to use-after-free bugs. This bug was introduced in Cranelift's migration to the regalloc2 register allocator in the Wasmtime 0.37.0 release on 2022-05-20. This bug has been patched and users should upgrade to Wasmtime version 0.38.2.
Mitigations for this issue can be achieved by doing one of:
- Disabling the reference types proposal by passing
falsetowasmtime::Config::wasm_reference_types. - Downgrading to Wasmtime 0.36.0 or prior.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | wasmtime | ≥ 0.37.0&&< 0.38.2 | 0.38.2 |
| 🦀crates.io | cranelift-codegen | ≥ 0.84.0&&< 0.85.2 | 0.85.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmtime. 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 wasmtime to 0.38.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-5fhj-g3p3-pq9g 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-5fhj-g3p3-pq9g 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-5fhj-g3p3-pq9g. 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-5fhj-g3p3-pq9g in your dependencies?
O3 detects GHSA-5fhj-g3p3-pq9g across crates.io dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.