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MEDIUM severity

Wasmtime vulnerable to Use After Free with `externref`sGHSA-5fhj-g3p3-pq9g

MEDIUMFix: bytecodealliance/wasmtime@2ba4bce

GHSA-5fhj-g3p3-pq9g is a medium-severity (CVSS 6.4) Use After Free vulnerability in wasmtime. A fix is available for wasmtime — see the affected versions and patch details below.

Also known asCVE-2022-31146RUSTSEC-2022-0100
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-5fhj-g3p3-pq9g.

EPSS Exploitation Probability

via FIRST.org ↗
1.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs70th percentile — riskier than 70% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected
🦀wasmtime🦀cranelift-codegen

Real-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:

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.iowasmtime≥ 0.37.0&&< 0.38.20.38.2cargo update -p wasmtime --precise 0.38.2
🦀crates.iocranelift-codegen≥ 0.84.0&&< 0.85.20.85.2cargo update -p cranelift-codegen --precise 0.85.2

Affected Products

2 products · 2 configurations
Application
cranelift-codegenbytecodealliance
≥ 0.84.0 && < 0.85.2
range
Application
wasmtimebytecodealliance
≥ 0.37.0 && < 0.38.2
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. 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.

  3. Workarounds

    Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Frequently Asked Questions

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
O3 Security · Impact-Aware SCA

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Wasmtime vulnerable to Use After Free with `externref`s