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.

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

EPSS: 0.001 (1.9th percentile) — read the EPSS interpretation.

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.

Affected products

Bytecodealliance Wasmtime — versions 43.0.0, >= 43.0.0, < 43.0.1

Weakness classification (CWE)

CWE-416 — Use After Free

References

security-advisories@github.com (x_refsource_CONFIRM, 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.