CVE-2026-34983 Wasmtime has a use-after-free bug after cloning `wasmtime::Linker`
A use-after-free vulnerability in Wasmtime allows host applications to trigger memory corruption via specific API calls, potentially leading to crashes or code execution.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-34983?
CVE-2026-34983 is a low-severity use after free 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. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. Specifically, the following steps must occur to trigger the bug clone a wasmtime::Linker, drop the original linker instance, use the new, cloned linker instance, resulting in a use-after-free. This vulnerability is fixed in 43.0.1.
Weakness: CWE-416
Which versions are affected by CVE-2026-34983?
4 open source packages ship an affected version, including wasmtime. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
wasmtime PyPI | All versions to 43.0.0 | None |
wasmtime crates.io | From 43.0.0 | 43.0.1 |
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-2026-34983?
Upgrade wasmtime to 43.0.1 or later.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-34983 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-34983 exists.
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-2026-34983, GHSA-hfr4-7c6c-48w2, PYSEC-2026-151, RUSTSEC-2026-0090, UBUNTU-CVE-2026-34983.