# 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.

- **Severity:** Medium 4.1 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **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:** Yes
- **Published:** 9 Apr 2026
- **Updated:** 13 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-34944, GHSA-qqfj-4vcm-26hv, JLSEC-2026-1357, RUSTSEC-2026-0087, UBUNTU-CVE-2026-34944

## 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 (Uncaught Exception)

## Which versions are affected by CVE-2026-34944?

9 open source packages ship an affected version, including wasmtime. It affects 1 product.


| Package | Ecosystem | 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 |
| `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: 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.

## 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](https://insights.sbomify.com/CVE-2026-34971/): Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift (critical 9.0)
- [CVE-2026-34987](https://insights.sbomify.com/CVE-2026-34987/): Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access (critical 9.0)
- [CVE-2022-39393](https://insights.sbomify.com/CVE-2022-39393/): Wasmtime vulnerable to data leakage between instances in the pooling allocator (high 8.6)
- [CVE-2022-24791](https://insights.sbomify.com/CVE-2022-24791/): Use after free in Wasmtime (high 8.1)
- [CVE-2026-47261](https://insights.sbomify.com/CVE-2026-47261/): Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34944 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-34944 in the wild and no public exploit code.

Affected packages and fixed versions:
- wasmtime (crates.io): affected all versions; fixed in 24.0.7
- wasmtime (crates.io): affected all versions; fixed in 24.0.7
- wasmtime (crates.io): affected from 0.0.0-0; fixed in 24.0.7, 36.0.7, 42.0.2, 43.0.1
- wasmtime (crates.io): affected from 25.0.0; fixed in 36.0.7
- wasmtime (crates.io): affected from 25.0.0; fixed in 36.0.7
- wasmtime (crates.io): affected from 37.0.0; fixed in 42.0.2
- wasmtime (crates.io): affected from 37.0.0; fixed in 42.0.2
- wasmtime (crates.io): affected from 43.0.0; fixed in 43.0.1
- wasmtime (crates.io): affected from 43.0.0; fixed in 43.0.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-34944/ (Markdown: https://insights.sbomify.com/CVE-2026-34944/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34944
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34944
- OSV: https://osv.dev/vulnerability/CVE-2026-34944

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34944/
Summaries are generated and may contain mistakes; the official description above is the record.