What’s Vulnerable › Vulnerabilities

CVE-2026-115889: Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation

• Severity: critical (CVSS 9.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-23 · updated 2026-10-26
• Weakness: CWE-197

Description

Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.

Affected products

• bytecodealliance wasmtime: before 36.0.19; from 37.0.0, < 43.0.0

References

• https://github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0
• https://github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
• https://github.com/bytecodealliance/wasmtime/pull/12613
• https://github.com/bytecodealliance/wasmtime/pull/14818
• https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19
• https://github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0
• https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm

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