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fkie_cve-2026-115889

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.

GHSA-897f-g5gm-fmxm — Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation

Affected: crates.io: wasmtime

## Summary

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.

## Impact

A Wasmtime engine with default settings (using the Cranelift backend) on any architecture/platform could experience a sandbox escape from a specially-crafted Wasm module.

## Patches

Wasmtime v36.0.19 has been released which fixes this issue.

RUSTSEC-2026-0380 — Bit-packing in Cranelift compiler causes silent overflow and miscompilation

Affected: crates.io: wasmtime

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm For more information see the GitHub-hosted security advisory.