# Wasmtime out-of-bounds zero-length stream writes panic

Source: https://junglewise.ai/threats/rustsec-2026-0357-out-of-bounds-zero-length-stream-writes-can-panic-2c07c43f  
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 that executes untrusted code. A flaw in stream write operations can cause the runtime to crash when processing certain zero-length writes, leading to denial of service of applications using Wasmtime to run WebAssembly modules.

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 to 48.0.5, 49.0.0 to 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, 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

An out-of-bounds memory access occurs during zero-length stream write operations in Wasmtime, triggered by insufficient bounds checking in the vulnerable code path. The vulnerability requires low privileges and passive user interaction (processing a malicious WebAssembly module). An attacker can crash the Wasmtime runtime, causing availability impact to the vulnerable system.

## Affected products

- Bytecode Alliance Wasmtime 46.0.0 to 48.0.5, 49.0.0 to 49.0.2

## Identifiers

- GHSA-93g3-36p8-x2gc
- RUSTSEC-2026-0357

## 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-2026-0357.html](https://rustsec.org/advisories/RUSTSEC-2026-0357.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)