Use After Free in Bytecodealliance Wasmtime
CVE-2026-34983
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.
Vulnerability class: Use-After-Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.0 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.001 (1.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 2nd percentile — 1.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: +0.000
Affected products
- Bytecodealliance Wasmtime — versions 43.0.0, >= 43.0.0, < 43.0.1
Weakness classification (CWE)
References
- github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hfr4-7c6c-48w2 (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-34983?
- CVE-2026-34983 is a medium-severity vulnerability in Bytecodealliance Wasmtime, classified under Use After Free. CVSS score: 5.0/10. Published 2026-04-09.
- How severe is CVE-2026-34983?
- Medium severity. CVSS v3 base score is 5.0 out of 10.