GHSA-q879-9g95-56mx
MEDIUMWrong type for `Linker`-define functions when used across two `Engine`s
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
wasmtime🐍wasmtimeReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io, PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
As a Rust library the wasmtime crate clearly marks which functions are safe and which are unsafe, guaranteeing that if consumers never use unsafe then it should not be possible to have memory unsafety issues in their embeddings of Wasmtime. An issue was discovered in the safe API of Linker::func_* APIs. These APIs were previously not sound when one Engine was used to create the Linker and then a different Engine was used to create a Store and then the Linker was used to instantiate a module into that Store. Cross-Engine usage of functions is not supported in Wasmtime and this can result in type confusion of function pointers, resulting in being able to safely call a function with the wrong type.
Triggering this bug requires using at least two Engine values in an embedding and then additionally using two different values with a Linker (one at the creation time of the Linker and another when instantiating a module with the Linker).
It's expected that usage of more-than-one Engine in an embedding is relatively rare since an Engine is intended to be a globally shared resource, so the expectation is that the impact of this issue is relatively small.
The fix implemented is to change this behavior to panic!() in Rust instead of silently allowing it. Using different Engine instances with a Linker is a programmer bug that wasmtime catches at runtime.
Patches
This bug has been patched and users should upgrade to Wasmtime version 0.30.0.
Workarounds
If you cannot upgrade Wasmtime and are using more than one Engine in your embedding it's recommended to instead use only one Engine for the entire program if possible. An Engine is designed to be a globally shared resource that is suitable to have only one for the lifetime of an entire process. If using multiple Engines is required then code should be audited to ensure that Linker is only used with one Engine.
For more information
If you have any questions or comments about this advisory:
- Reach out to us on the Bytecode Alliance Zulip chat
- Open an issue in the
bytecodealliance/wasmtimerepository
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | wasmtime | all versions | 0.30.0 |
| 🐍PyPI | wasmtime | all versions | 0.30.0 |
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 0.30.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q879-9g95-56mx 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-q879-9g95-56mx 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-q879-9g95-56mx. 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-q879-9g95-56mx in your dependencies?
O3 detects GHSA-q879-9g95-56mx across crates.io, PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.