CVE-2026-115889: Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
In Wasmtime prior to v43, the Cranelift compiler backend bit-packs its SSA value indices in a way that can result in silent overflow in release builds, and result in incorrect value references in the IR resulting in arbitrary miscompilation. A very large Wasm function body, or one that is specially crafted to use many SSA values, can use this to force type-confusion or other arbitrary side-effects and escape the sandbox.
Cranelift was changed in Wasmtime v43 to use a full u32 index, with checks if that limit is exceeded, and so is no longer susceptible to this bug.
References
- github.com/advisories/GHSA-897f-g5gm-fmxm
- github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0
- github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
- github.com/bytecodealliance/wasmtime/pull/12613
- github.com/bytecodealliance/wasmtime/pull/14818
- github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19
- github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0
- github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm
- nvd.nist.gov/vuln/detail/CVE-2026-115889
- rustsec.org/advisories/RUSTSEC-2026-0380.html
Code Behaviors & Features
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