GHSA-gwc9-348x-qwv2 is a high-severity (CVSS 8.1) Use After Free vulnerability in wasmtime. A fix is available for wasmtime — see the affected versions and patch details below.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
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Real-World Exposure
wasmtime🦀wasmtimeReal-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 use after free vulnerability in Wasmtime when both running Wasm that uses externrefs and enabling epoch interruption in Wasmtime. If you are not explicitly enabling epoch interruption (it is disabled by default) then you are not affected. If you are explicitly disabling the Wasm reference types proposal (it is enabled by default) then you are also not affected.
The use after free is caused by Cranelift failing to emit stack maps when there are safepoints inside cold blocks. Cold blocks occur when epoch interruption is enabled. Cold blocks are emitted at the end of compiled functions, and change the order blocks are emitted versus defined. This reordering accidentally caused Cranelift to skip emitting some stack maps because it expected to emit the stack maps in block definition order, rather than block emission order. When Wasmtime would eventually collect garbage, it would fail to find live references on the stack because of the missing stack maps, think that they were unreferenced garbage, and therefore reclaim them. Then after the collection ended, the Wasm code could use the reclaimed-too-early references, which is a use after free.
This bug was discovered while extending our fuzz targets for externrefs and GC in Wasmtime. The updated fuzz target thoroughly exercises these code paths and feature combinations now. We have also added a regression test for this bug. Released versions 0.34.2 and 0.35.2, which fix the vulnerability. We recommend all Wasmtime users upgrade to these patched versions. If upgrading is not an option for you at this time, you can avoid the vulnerability by either disabling the Wasm reference types proposal or by disabling epoch interruption if you were previously enabling it.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | wasmtime | all versions | 0.34.2cargo update -p wasmtime --precise 0.34.2 |
| 🦀crates.io | wasmtime | ≥ 0.35.0&&< 0.35.2 | 0.35.2cargo update -p wasmtime --precise 0.35.2 |
Affected Products
wasmtimebytecodeallianceDetection & mitigation playbook
Open-source dependencyDetect
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.
Fix
Update wasmtime to 0.34.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-gwc9-348x-qwv2 is resolved across your whole dependency graph.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Frequently Asked Questions
Is GHSA-gwc9-348x-qwv2 in your dependencies?
Find it across crates.io, including transitive dependencies.