Vulnerability in Bytecodealliance Wasmtime
CVE-2026-34942
Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of transcoding strings into the Component Model's utf16 or latin1+utf16 encodings improperly verified the alignment of reallocated strings. This meant that unaligned pointers could be passed to the host for transcoding which would trigger a host panic. This panic is possible to trigger from malicious guests which transfer very specific strings across components with specific addresses. Host panics are considered a DoS vector in Wasmtime as the panic conditions are controlled by the guest in this situation. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.004 (34.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 34.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.001
Affected products
- Bytecodealliance Wasmtime — versions < 24.0.7, >= 25.0.0, < 36.0.7, >= 37.0.0, < 42.0.2
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-34942?
- CVE-2026-34942 is a medium-severity vulnerability in Bytecodealliance Wasmtime, classified under Improper Validation of Array Index. CVSS score: 6.5/10. Published 2026-04-09.
- How severe is CVE-2026-34942?
- Medium severity. CVSS v3 base score is 6.5 out of 10.