# Wasmtime type confusion with host-created struct types

Source: https://junglewise.ai/threats/rustsec-2026-0423-cross-engine-type-confusion-with-host-created-struct-89fe3f0e  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-29. Updated: 2026-11-01  
License: CC BY 4.0 with a link back

Severity: info · Published 2026-10-29

Wasmtime is a WebAssembly runtime that executes untrusted code. A type confusion vulnerability in how host-created struct types with supertypes are handled across different engine instances could allow an attacker to bypass type safety checks and potentially execute arbitrary code or cause memory corruption.

Technologies: [Bytecode Alliance Wasmtime](https://junglewise.ai/threats/technologies/bytecode-alliance-wasmtime), [wasmtime (crates.io)](https://junglewise.ai/threats/technologies/wasmtime). Vendors: [Bytecode Alliance](https://junglewise.ai/threats/vendors/bytecode-alliance), [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, published 29 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime 47.0.0–48.0.7, 49.0.0–49.0.4, 50.0.0; wasmtime (crates.io) SEMVER:introduced=47.0.0,fixed=48.0.8,introduced=49.0.0,fixed=49.0.5,introduced=50.0.0,fixed=50.0.1.

**Is there a fix for This vulnerability?** Yes. wasmtime (crates.io): upgrade to 50.0.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network or with local access, in a software library.

**Am I affected?** Check whether you run Bytecode Alliance 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 50.0.1 or later

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


## Technical details

A cross-engine type confusion flaw exists in Wasmtime's handling of host-created struct types that use supertypes when accessed across different engine instances. The vulnerability allows type confusion attacks that break WebAssembly's type safety guarantees. The issue requires the attacker to control both WebAssembly code and struct type creation across multiple engines.

## Affected products

- Bytecode Alliance Wasmtime 47.0.0–48.0.7, 49.0.0–49.0.4, 50.0.0

## Identifiers

- GHSA-qw58-7h65-crq2
- RUSTSEC-2026-0423

## Timeline

- 2026-10-29: disclosed
- 2026-10-30: advisory

## References

- [https://crates.io/crates/wasmtime](https://crates.io/crates/wasmtime)
- [https://rustsec.org/advisories/RUSTSEC-2026-0423.html](https://rustsec.org/advisories/RUSTSEC-2026-0423.html)

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- [Wasmtime denial of service via thread.yield in component start](https://junglewise.ai/threats/cve-2026-119140-wasmtime-46-0-0-before-48-0-6-and-49-0-0-before-49-0-3-contains)