# CVE-2026-119135: Wasmtime panic in component model stream type mismatch

Source: https://junglewise.ai/threats/cve-2026-119135-wasmtime-46-0-0-before-48-0-6-and-49-0-0-before-49-0-3-panics  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-29. Updated: 2026-10-29  
License: CC BY 4.0 with a link back

CVE-2026-119135 · Severity: medium · CVSS 4.8 · Published 2026-10-29

Wasmtime is a WebAssembly runtime that executes untrusted code within applications. When host code reads a component model stream with a different Rust type than it was originally created with, Wasmtime panics and crashes the embedding process. This allows guest WebAssembly code to cause a denial of service by returning streams that the host reads as the wrong type.

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-2026-119135 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-119135 being exploited in the wild.

**How severe is CVE-2026-119135?** Medium severity, with a CVSS score of 4.8, published 29 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime 46.0.0 before 48.0.6, 49.0.0 before 49.0.3.

**Is there a fix for CVE-2026-119135?** Yes: fixed in 48.0.6, 49.0.3. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-119135 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-119135?** 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 48.0.6, 49.0.3

## Technical details

The vulnerability occurs in Wasmtime's component model stream handling when a StreamReader is created as one type (T) and later read as a different type (U) that maps to the same component model type. The host-to-host read path asserts matching Rust TypeIds instead of returning an error, causing a panic. An attacker controlling guest code can trigger this by returning a stream with a type mismatch, crashing the host process.

## Affected products

- Bytecode Alliance Wasmtime 46.0.0 before 48.0.6, 49.0.0 before 49.0.3

## Timeline

- 2026-10-29: advisory
- 2026-10-14: disclosed

## References

- [https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-63h4-6cx9-pjfj](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-63h4-6cx9-pjfj)
- [https://www.vulncheck.com/advisories/wasmtime-46.0.0-before-48.0.6-and-49.0.0-before-49.0.3-panic-via-streamreader-type-mismatch](https://www.vulncheck.com/advisories/wasmtime-46.0.0-before-48.0.6-and-49.0.0-before-49.0.3-panic-via-streamreader-type-mismatch)

## 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)