# 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.

- **Severity:** Low 1.0 (`CVSS:4.0/AV:P/AC:H/AT:P/PR:H/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N`)
- **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:** Yes
- **Published:** 9 Apr 2026
- **Updated:** 13 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-34983, GHSA-hfr4-7c6c-48w2, PYSEC-2026-151, RUSTSEC-2026-0090, UBUNTU-CVE-2026-34983

## 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 (Use After Free)

## Which versions are affected by CVE-2026-34983?

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


| Package | Ecosystem | 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: Bytecodealliance Wasmtime.

## How do I fix CVE-2026-34983?

Upgrade wasmtime to 43.0.1 or later.

## 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](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-2026-34983 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-34983 exists.

Affected packages and fixed versions:
- wasmtime (PyPI): affected all versions up to 43.0.0; no fix listed
- 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
- 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-2026-34983/ (Markdown: https://insights.sbomify.com/CVE-2026-34983/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34983
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34983
- OSV: https://osv.dev/vulnerability/CVE-2026-34983

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34983/
Summaries are generated and may contain mistakes; the official description above is the record.