Wasmtime panics when transcoding misaligned utf-16 strings_CVE-2026-34942

5.9 / 10

MEDIUM

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L

Description

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.

Basic Information

ID CVE-2026-34942

Source GitHub_M

Published Apr 9, 2026 at 18:32

Modified Apr 9, 2026 at 19:36

Affected Product

Vendor bytecodealliance

Product wasmtime

Version < 24.0.7

Affected Versions bytecodealliance wasmtime < 24.0.7
bytecodealliance wasmtime >= 25.0.0, < 36.0.7
bytecodealliance wasmtime >= 37.0.0, < 42.0.2
bytecodealliance wasmtime >= 43.0.0, < 44.0.1

CWE Classification

CWE-129

References

github.com /bytecodealliance/wasmtime/security/advisories/GHSA-jxhv-7h78-9775

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    "published": "2026-04-09T18:32:56.456Z",
    "modified": "2026-04-09T19:36:13.614Z",
    "type": "cve",
    "title": "Wasmtime panics when transcoding misaligned utf-16 strings",
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