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

• crates.io wasmtime: < 36.0.19 → fixed in 36.0.19 • crates.io wasmtime: >= 37.0.0, < 43.0.0 → fixed in 43.0.0

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.