# Wasmtime component async-lifted callback stack buffer overflow

Source: https://junglewise.ai/threats/rustsec-2026-0327-wasmtime-component-async-lifted-callback-result-count-c802aa47  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-02. Updated: 2026-10-04  
License: CC BY 4.0 with a link back

Severity: medium · CVSS 4 · Published 2026-10-02

Wasmtime is a WebAssembly runtime that executes sandboxed code. When processing async-lifted callbacks in WebAssembly components, the system fails to validate the number of result values, allowing an attacker to trigger a native stack buffer overflow. This can lead to code execution, data corruption, or system crashes.

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 2 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime 39.0.0 to 48.0.3, 49.0.0 to 49.0.1; wasmtime (crates.io) SEMVER:introduced=39.0.0,fixed=48.0.4,introduced=49.0.0,fixed=49.0.2.

**Is there a fix for This vulnerability?** Yes. wasmtime (crates.io): upgrade to 49.0.2 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 49.0.2 or later

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


## Technical details

The vulnerability exists in Wasmtime's component model implementation where async-lifted callback result counts are not validated before being used to write to the stack. An unauthenticated remote attacker can provide a malformed WebAssembly component over the network that triggers the unvalidated code path, causing a stack buffer overflow that enables arbitrary code execution or denial of service.

## Affected products

- Bytecode Alliance Wasmtime 39.0.0 to 48.0.3, 49.0.0 to 49.0.1

## Identifiers

- GHSA-32h6-97mm-8q3c
- RUSTSEC-2026-0327

## Timeline

- 2026-10-02: disclosed
- 2026-10-02: advisory

## References

- [https://crates.io/crates/wasmtime](https://crates.io/crates/wasmtime)
- [https://rustsec.org/advisories/RUSTSEC-2026-0327.html](https://rustsec.org/advisories/RUSTSEC-2026-0327.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)