# CVE-2026-34946: Wasmtime has host panic when Winch compiler executes `table.fill`

Source: https://junglewise.ai/threats/cve-2026-34946-wasmtime-has-host-panic-when-winch-compiler-executes-table-fill  
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-2026-34946 · Severity: high · CVSS 7.5 · Published 2026-04-09

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler contains a vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring changed how compiled code referenced tables within the table.* instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. This vulnerability is fixed in 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-2026-34946 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34946 being exploited in the wild.

**How severe is CVE-2026-34946?** High severity, with a CVSS score of 7.5, published 9 April 2026.

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

**Is there a fix for CVE-2026-34946?** Yes. wasmtime (crates.io): upgrade to 36.0.7, 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-2026-34946?** 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 36.0.7, 43.0.1 or later

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


## Affected products

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

## Identifiers

- CVE-2026-34946
- GHSA-q49f-xg75-m9xw
- RUSTSEC-2026-0089

## References

- [https://api.github.com/users/shumbo](https://api.github.com/users/shumbo)
- [https://github.com/shumbo](https://github.com/shumbo)
- [https://api.github.com/users/shumbo/gists%7B/gist_id%7D](https://api.github.com/users/shumbo/gists%7B/gist_id%7D)
- [https://api.github.com/users/shumbo/repos](https://api.github.com/users/shumbo/repos)
- [https://avatars.githubusercontent.com/u/10496155?v=4](https://avatars.githubusercontent.com/u/10496155?v=4)
- [https://api.github.com/users/shumbo/events%7B/privacy%7D](https://api.github.com/users/shumbo/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)