# Wasmtime async-entrypoint requirement enforcement bypass

Source: https://junglewise.ai/threats/rustsec-2026-0362-wasmtime-may-not-properly-enforce-async-entrypoint-5479b21b  
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 or semi-trusted code in isolated environments. A failure to properly enforce async-entrypoint requirements could allow an attacker with low privileges to cause availability impact to the system, potentially disrupting service availability or enabling denial-of-service attacks.

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 42.0.0-48.0.5, 49.0.0-49.0.2; wasmtime (crates.io) SEMVER:introduced=42.0.0,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, 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 49.0.3 or later

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


## Technical details

Wasmtime versions 42.0.0 through 48.0.5 and 49.0.0 through 49.0.2 fail to properly enforce async-entrypoint requirements, which are restrictions on how WebAssembly functions can be invoked asynchronously. An attacker with low privileges and user interaction can exploit this over the network to impact system availability. The vulnerability stems from improper validation of async invocation constraints.

## Affected products

- Bytecode Alliance Wasmtime 42.0.0-48.0.5, 49.0.0-49.0.2

## Identifiers

- GHSA-vcg5-q8m5-8379
- RUSTSEC-2026-0362

## 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-2026-0362.html](https://rustsec.org/advisories/RUSTSEC-2026-0362.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)