CVE-2026-115889 Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-115889?
CVE-2026-115889 is a critical vulnerability in bytecodealliance wasmtime, published on 23 Oct 2026.
Official 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.
Which versions are affected by CVE-2026-115889?
5 open source packages ship an affected version, including wasmtime.
| Package | Affected | Fixed in |
|---|---|---|
wasmtime crates.io | All versions | 36.0.19 |
wasmtime crates.io | All versions | 36.0.19 |
wasmtime crates.io | From 0.0.0-0 | 36.0.19, 43.0.0 |
wasmtime crates.io | From 37.0.0 | 43.0.0 |
wasmtime crates.io | From 37.0.0 | 43.0.0 |
How do I fix CVE-2026-115889?
Upgrade wasmtime to a fixed version for your release line: 36.0.19 or 43.0.0.
Is CVE-2026-115889 being exploited?
There is no known exploitation of CVE-2026-115889 in the wild and no public exploit code.
Public exploit code: 2 proofs of concept on GitHub.
Sources
Also known as AZL-111431, AZL-111437, DEBIAN-CVE-2026-115889, GHSA-897f-g5gm-fmxm, RUSTSEC-2026-0380, UBUNTU-CVE-2026-115889.