CVE-2026-34944 Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64
Attackers can cause a segfault or read out-of-sandbox memory in Wasmtime on x86-64 when SSE3 is disabled and specific trap configurations are used.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-34944?
CVE-2026-34944 is a medium-severity memory corruption vulnerability in bytecodealliance wasmtime, published on 9 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, On x86-64 platforms with SSE3 disabled Wasmtime's compilation of the f64x2.splat WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages disabled it's possible for out-of-sandbox data to be loaded, but this data is not visible to WebAssembly guests. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.
Weakness: CWE-248
Which versions are affected by CVE-2026-34944?
9 open source packages ship an affected version, including wasmtime. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
wasmtime crates.io | All versions | 24.0.7 |
wasmtime crates.io | All versions | 24.0.7 |
wasmtime crates.io | From 0.0.0-0 | 24.0.7, 36.0.7, 42.0.2, 43.0.1 |
wasmtime crates.io | From 25.0.0 | 36.0.7 |
wasmtime crates.io | From 25.0.0 | 36.0.7 |
wasmtime crates.io | From 37.0.0 | 42.0.2 |
3 more packages
wasmtime crates.io | From 37.0.0 | 42.0.2 |
wasmtime crates.io | From 43.0.0 | 43.0.1 |
wasmtime crates.io | From 43.0.0 | 43.0.1 |
Products include Bytecodealliance Wasmtime.
How do I fix CVE-2026-34944?
Upgrade wasmtime to a fixed version for your release line: 24.0.7, 36.0.7, 42.0.2 or 43.0.1.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-34944 being exploited?
There is no known exploitation of CVE-2026-34944 in the wild and no public exploit code.
Other vulnerabilities in bytecodealliance wasmtime
- CVE-2026-34971 Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift
- CVE-2026-34987 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access
- CVE-2022-39393 Wasmtime vulnerable to data leakage between instances in the pooling allocator
- CVE-2022-24791 Use after free in Wasmtime
- CVE-2026-47261 Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction
Sources
Also known as DEBIAN-CVE-2026-34944, GHSA-qqfj-4vcm-26hv, JLSEC-2026-1357, RUSTSEC-2026-0087, UBUNTU-CVE-2026-34944.