CVE-2026-34942CWE-129

Wasmtime panics when transcoding misaligned utf-16 strings

Medium · published April 9, 2026

CVSS v4.0
5.9
EPSS
0%
Percentile
35.2
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
5.9 · MEDIUM
Vector
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
EPSS
0.00420 · 35.2th percentile
Weakness
CWE-129 · Improper Validation of Array Index
Published
2026-04-09T18:32Z
EPSS history
Timeline
  • 09 APR 18:32Z
    Wasmtime panics when transcoding misaligned utf-16 strings
    cvelistv5