# Wasmtime host panic in call_async cancellation

Source: https://junglewise.ai/threats/rustsec-2026-0354-host-panic-when-component-call-async-is-cancelled-d72bda55  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-14. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

Severity: medium · CVSS 4 · Published 2026-10-14

Wasmtime is a WebAssembly runtime used to execute untrusted code. Under specific conditions when an asynchronous component call is cancelled, the host process can panic, causing a denial of service. An attacker with low privileges and the ability to trigger component cancellation could crash the application.

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?** Medium severity, with a CVSS score of 4, published 14 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime 46.0.0 through 48.0.5, 49.0.0 through 49.0.2; wasmtime (crates.io) SEMVER:introduced=46.0.0,fixed=48.0.6,introduced=49.0.0,fixed=49.0.3.

**Is there a fix for This vulnerability?** Yes. wasmtime (crates.io): upgrade to 49.0.3 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.

**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 49.0.3 or later

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


## Technical details

A panic occurs in Wasmtime's `call_async` component function when cancellation is triggered under certain conditions. The vulnerability requires network access, low privileges, passive user interaction, and specific attack prerequisites. Successful exploitation results in denial of service to the host system through an unhandled panic.

## Affected products

- Bytecode Alliance Wasmtime 46.0.0 through 48.0.5, 49.0.0 through 49.0.2

## Identifiers

- GHSA-3r89-v5mq-j5xf
- RUSTSEC-2026-0354

## Timeline

- 2026-10-14: disclosed
- 2026-10-14: advisory

## References

- [https://crates.io/crates/wasmtime](https://crates.io/crates/wasmtime)
- [https://rustsec.org/advisories/RUSTSEC-2026-0354.html](https://rustsec.org/advisories/RUSTSEC-2026-0354.html)

## Related threats

- [Wasmtime wasi-http response splitting via unvalidated headers](https://junglewise.ai/threats/cve-2026-121439-wasmtime-46-0-0-before-48-0-7-and-49-0-0-before-49-0-4-contains)
- [Wasmtime denial of service in component model stream operations](https://junglewise.ai/threats/cve-2026-119143-wasmtime-46-0-0-before-48-0-6-and-49-0-0-before-49-0-3-contains)
- [Wasmtime host panic in call_async Future drop](https://junglewise.ai/threats/cve-2026-119142-wasmtime-46-0-0-before-48-0-6-and-49-0-0-before-49-0-3-contains)
- [Wasmtime denial of service in realloc handling](https://junglewise.ai/threats/cve-2026-119141-wasmtime-46-0-0-before-48-0-6-and-49-0-0-before-49-0-3-contains)
- [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)