# CVE-2026-34942: Wasmtime: Panic when transcoding misaligned utf-16 strings

Source: https://junglewise.ai/threats/cve-2026-34942-wasmtime-panic-when-transcoding-misaligned-utf-16-strings  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-09. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

CVE-2026-34942 · Severity: medium · CVSS 6.5 · Published 2026-04-09

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.

Technologies: [Bytecodealliance Wasmtime](https://junglewise.ai/threats/technologies/bytecodealliance-wasmtime), [wasmtime (crates.io)](https://junglewise.ai/threats/technologies/wasmtime). Vendors: [Bytecodealliance](https://junglewise.ai/threats/vendors/bytecodealliance), [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is CVE-2026-34942 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34942 being exploited in the wild.

**How severe is CVE-2026-34942?** Medium severity, with a CVSS score of 6.5, published 9 April 2026.

**Which products and versions are affected?** wasmtime (crates.io) SEMVER:introduced=0,fixed=24.0.7, SEMVER:introduced=0.0.0-0,fixed=24.0.7,introduced=25.0.0,fixed=36.0.7,introduced=37.0.0,fixed=42.0.2,introduced=43.0.0,fixed=43.0.1.

**Is there a fix for CVE-2026-34942?** Yes. wasmtime (crates.io): upgrade to 24.0.7, 43.0.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-34942?** Check whether you run Bytecodealliance Wasmtime or wasmtime (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- wasmtime (crates.io): upgrade to 24.0.7, 43.0.1 or later

  ```sh
  cargo update -p wasmtime
  ```


## Affected products

- Bytecodealliance Wasmtime
- wasmtime (crates.io) SEMVER:introduced=0,fixed=24.0.7, SEMVER:introduced=0.0.0-0,fixed=24.0.7,introduced=25.0.0,fixed=36.0.7,introduced=37.0.0,fixed=42.0.2,introduced=43.0.0,fixed=43.0.1

## Identifiers

- CVE-2026-34942
- GHSA-jxhv-7h78-9775
- RUSTSEC-2026-0092

## References

- [https://api.github.com/users/alexcrichton](https://api.github.com/users/alexcrichton)
- [https://github.com/alexcrichton](https://github.com/alexcrichton)
- [https://api.github.com/users/alexcrichton/gists%7B/gist_id%7D](https://api.github.com/users/alexcrichton/gists%7B/gist_id%7D)
- [https://api.github.com/users/alexcrichton/repos](https://api.github.com/users/alexcrichton/repos)
- [https://avatars.githubusercontent.com/u/64996?v=4](https://avatars.githubusercontent.com/u/64996?v=4)
- [https://api.github.com/users/alexcrichton/events%7B/privacy%7D](https://api.github.com/users/alexcrichton/events%7B/privacy%7D)

## Related threats

- [RUSTSEC-2026-0422 - Typed functions with `i31` or `nullref` arguments may panic due to insufficient type-check](https://junglewise.ai/threats/rustsec-2026-0422-typed-functions-with-i31-or-nullref-arguments-may-0545dc2b)
- [Wasmtime type confusion with host-created struct types](https://junglewise.ai/threats/rustsec-2026-0423-cross-engine-type-confusion-with-host-created-struct-89fe3f0e)
- [Wasmtime unchecked memory usage in borrowed resource transfer](https://junglewise.ai/threats/rustsec-2026-0424-unchecked-memory-usage-in-transferring-borrowed-b297503c)
- [Wasmtime Cranelift aarch64 br_table sandbox escape](https://junglewise.ai/threats/cve-2026-115893-wasmtime-is-a-runtime-for-webassembly-prior-to-36-0-19-48-0-7)
- [Wasmtime component-model type-check bypass in stream/future lowering](https://junglewise.ai/threats/cve-2026-115892-wasmtime-is-a-runtime-for-webassembly-from-46-0-0-until-48-0-7)