CVE-2026-34942: Bytecodealliance Wasmtime

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Bytecodealliance Wasmtime: before 24.0.7 (fixed in 24.0.7); from 25.0.0, before 36.0.7 (fixed in 36.0.7); from 37.0.0, before 42.0.2 (fixed in 42.0.2); from 43.0.0, before 43.0.1 (fixed in 43.0.1)

Published 2026-04-09. Last modified 2026-06-17.