CVE-2022-31104 is a medium-severity (CVSS 4.8) CWE-682 vulnerability in wasmtime. A fix is available for wasmtime — see the affected versions and patch details below.
Miscompilation of `i8x16.swizzle` and `select` with v128 inputs in Wasmtime
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 CVE-2022-31104.
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.
How urgent is this, really
CVE-2022-31104 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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
Impact
Wasmtime's implementation of the SIMD proposal for WebAssembly on x86_64 contained two distinct bugs in the instruction lowerings implemented in Cranelift. The aarch64 implementation of the simd proposal is not affected. The bugs were presented in the i8x16.swizzle and select WebAssembly instructions. The select instruction is only affected when the inputs are of v128 type. The correspondingly affected Cranelift instructions were swizzle and select.
The swizzle instruction lowering in Cranelift erroneously overwrote the mask input register which could corrupt a constant value, for example. This means that future uses of the same constant may see a different value than the constant itself.
The select instruction lowering in Cranelift wasn't correctly implemented for vector types that are 128-bits wide. When the condition was 0 the wrong instruction was used to move the correct input to the output of the instruction meaning that only the low 32 bits were moved and the upper 96 bits of the result were left as whatever the register previously contained (instead of the input being moved from). The select instruction worked correctly if the condition was nonzero, however.
This bug in Wasmtime's implementation of these instructions on x86_64 represents an incorrect implementation of the specified semantics of these instructions according to the WebAssembly specification. The impact of this is benign for hosts running WebAssembly but represents possible vulnerabilities within the execution of a guest program. For example a WebAssembly program could take unintended branches or materialize incorrect values internally which runs the risk of exposing the program itself to other related vulnerabilities which can occur from miscompilations.
Patches
We have released Wasmtime 0.38.1 and cranelift-codegen (and other associated cranelift crates) 0.85.1 which contain the corrected implementations of these two instructions in Cranelift.
Workarounds
If upgrading is not an option for you at this time, you can avoid the vulnerability by disabling the Wasm simd proposal
config.wasm_simd(false);
Additionally the bug is only present on x86_64 hosts. Other aarch64 hosts are not affected. Note that s390x hosts don't yet implement the simd proposal and are not affected.
References
- The WebAssembly simd proposal
- Original test case showing the erroneous behavior
- Fix for the
swizzleinstruction - Fix for the
selectinstruction
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/wasmtime repository
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | wasmtime | all versions | 0.38.1cargo update -p wasmtime --precise 0.38.1 |
| 🦀crates.io | cranelift-codegen | all versions | 0.85.1cargo update -p cranelift-codegen --precise 0.85.1 |
Detection & 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 0.38.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2022-31104 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2022-31104 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2022-31104. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2022-31104 in your dependencies?
O3 Security finds CVE-2022-31104 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.