{"id":"CVE-2026-115889","aliases":["GHSA-897f-g5gm-fmxm"],"title":"Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation","summary":"Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation","severity":"critical","cvss":9.9,"cwe":["CWE-197","CWE-843"],"vendor":"wasmtime","product":"wasmtime","ecosystem":"rust","affected":["wasmtime < 36.0.19","wasmtime >= 37.0.0, < 43.0.0"],"patched":["wasmtime 36.0.19","wasmtime 43.0.0"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T22:02:21Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-897f-g5gm-fmxm","references":[{"url":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm"},{"url":"https://github.com/bytecodealliance/wasmtime/pull/12613"},{"url":"https://github.com/bytecodealliance/wasmtime/pull/14818"},{"url":"https://github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0"},{"url":"https://github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa"},{"url":"https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19"},{"url":"https://github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0"},{"url":"https://rustsec.org/advisories/RUSTSEC-2026-0380.html"},{"url":"https://github.com/advisories/GHSA-897f-g5gm-fmxm"}],"tags":["ghsa","rust","cve.org"],"ingestedAt":"2026-10-23T21:38:13.047Z","slug":"CVE-2026-115889","body":"## Overview\n\n## Summary\n\nIn 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.\n\nCranelift 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.\n\n## Impact\n\nA Wasmtime engine with default settings (using the Cranelift backend) on any architecture/platform could experience a sandbox escape from a specially-crafted Wasm module.\n\n## Patches\n\nWasmtime v36.0.19 has been released which fixes this issue.\n\n## Affected packages\n\n- `wasmtime < 36.0.19`\n- `wasmtime >= 37.0.0, < 43.0.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `wasmtime 36.0.19`\n- `wasmtime 43.0.0`","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":54.5,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}