# CVE-2026-115384: Wasmtime stack buffer overflow in component async callbacks

Source: https://junglewise.ai/threats/cve-2026-115384-wasmtime-39-0-0-before-48-0-4-and-49-0-0-before-49-0-2-contains  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-22. Updated: 2026-10-22  
License: CC BY 4.0 with a link back

CVE-2026-115384 · Severity: critical · CVSS 9.9 · Published 2026-10-22

Wasmtime is a WebAssembly runtime that executes untrusted code in a sandbox. This vulnerability allows a malicious WebAssembly component to write up to 16KB of arbitrary data to the host's memory stack via mistyped async callback functions. An attacker can overwrite return addresses to crash the host, leak sensitive data, or escape the sandbox entirely.

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

## Quick answers

**Is CVE-2026-115384 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115384 being exploited in the wild.

**How severe is CVE-2026-115384?** Critical severity, with a CVSS score of 9.9, published 22 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime 39.0.0 before 48.0.4, 49.0.0 before 49.0.2.

**Is there a fix for CVE-2026-115384?** Yes: fixed in Wasmtime 48.0.4, 49.0.2. Until then: Disable the component-model-async feature to reject all async components, or use a patched version of wasmparser (v1.260.0 or later) to validate components before passing them to Wasmtime. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-115384 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-115384?** Check whether you run Bytecode Alliance Wasmtime 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

- Fixed in Wasmtime 48.0.4, 49.0.2

Disable the component-model-async feature to reject all async components, or use a patched version of wasmparser (v1.260.0 or later) to validate components before passing them to Wasmtime.

## Technical details

The vulnerability stems from incomplete validation in wasmparser of callback function type signatures for async-lifted exports in the component model, combined with missing runtime bounds checks in Wasmtime's host-to-guest trampoline code. An attacker can supply a component with an async callback function whose return type is not validated, allowing the guest to write beyond the allocated stack buffer when the callback returns. The attack requires the ability to supply a malicious WebAssembly component to the host; no authentication or user interaction is needed once the component is loaded.

## Affected products

- Bytecode Alliance Wasmtime 39.0.0 before 48.0.4, 49.0.0 before 49.0.2

## Timeline

- 2026-10-02: disclosed
- 2026-10-22: advisory

## References

- [https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-32h6-97mm-8q3c](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-32h6-97mm-8q3c)
- [https://www.vulncheck.com/advisories/wasmtime-39.0.0-before-48.0.4-and-49.0.0-before-49.0.2-stack-buffer-overflow](https://www.vulncheck.com/advisories/wasmtime-39.0.0-before-48.0.4-and-49.0.0-before-49.0.2-stack-buffer-overflow)

## 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)