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GHSA-jxhv-7h78-9775

Wasmtime: Panic when transcoding misaligned utf-16 strings

Source: GitHub Advisory Database (reviewed) Moderate CVE-2026-34942

Packages

EcosystemPackageAffectedFixed in
crates.io wasmtime < 24.0.7 24.0.7
crates.io wasmtime >= 25.0.0, < 36.0.7 36.0.7
crates.io wasmtime >= 37.0.0, < 42.0.2 42.0.2
crates.io wasmtime >= 43.0.0, < 43.0.1 43.0.1

Details

As written in the advisory (Markdown source, shown as plain text).

### 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.

References

External links from the advisory. They lead to third-party sites.