Vulnerability · Published Apr 9, 2026 · Assigned by GitHub_M
CVE-2026-34942Wasmtime panics when transcoding misaligned utf-16 strings
Medium 5.9
In plain English
A medium-severity security flaw in wasmtime from bytecodealliance. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 31% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | rust-wasmtime | no fix listed | DEBIAN-CVE-2026-34942 |
| Debian:14 | rust-wasmtime | 36.0.7+dfsg-1 | DEBIAN-CVE-2026-34942 |
| Ubuntu:24.04:LTS | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-34942 |
| Ubuntu:25.10 | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-34942 |
| Ubuntu:26.04:LTS | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-34942 |
| Ubuntu:26.10 | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-34942 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| bytecodealliance | wasmtime | < 24.0.7>= 25.0.0, < 36.0.7>= 37.0.0, < 42.0.2>= 43.0.0, < 44.0.1 |
Weakness: CWE-129 · 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