CVE-2026-34942: Wasmtime panics when transcoding misaligned utf-16 strings
Impact
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.
Patches
Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.
Workarounds
There is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.
Other sources
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.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-34942?
CVE-2026-34942 has a medium severity rating of 5.9 according to the CVSS score.
What is the impact of CVE-2026-34942?
CVE-2026-34942 can cause Wasmtime to panic when transcoding misaligned UTF-16 strings, leading to potential host panics.
How do I fix CVE-2026-34942?
To fix CVE-2026-34942, ensure you are using an updated version of Wasmtime that addresses the alignment verification issue.
Which software is affected by CVE-2026-34942?
CVE-2026-34942 affects the Wasmtime implementation in the Rust programming environment.
What types of vulnerabilities are associated with CVE-2026-34942?
CVE-2026-34942 is associated with out-of-bounds reads and buffer overflow vulnerabilities.