# wasmtime-wasi excessive memory allocation when guests lack stdio

Source: https://junglewise.ai/threats/rustsec-2026-0322-excessive-allocated-memory-on-the-host-when-guests-84ef0787  
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-wasi is a library that provides WebAssembly guests with POSIX-style input/output capabilities. When a WebAssembly guest module lacks standard input/output streams, the host system can be manipulated to excessively allocate memory, potentially leading to denial of service through memory exhaustion.

Technologies: [Bytecode Alliance Wasmtime-Wasi](https://junglewise.ai/threats/technologies/bytecode-alliance-wasmtime-wasi), [wasmtime-wasi (crates.io)](https://junglewise.ai/threats/technologies/wasmtime-wasi). 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-Wasi before 36.0.17; 37.0.0–48.0.3; 49.0.0–49.0.1; wasmtime-wasi (crates.io) SEMVER:introduced=0.0.0-0,fixed=36.0.17,introduced=37.0.0,fixed=48.0.4,introduced=49.0.0,fixed=49.0.2.

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

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


## Technical details

The vulnerability exists in wasmtime-wasi versions before 36.0.17, 37.0.0–48.0.3, and 49.0.0–49.0.1, where improper handling of guests without stdio causes unbounded memory allocation on the host. The issue is triggered via network attack vector with low privileges required and user interaction. An attacker gains the ability to cause high availability impact to the vulnerable system through memory exhaustion.

## Affected products

- Bytecode Alliance wasmtime-wasi before 36.0.17; 37.0.0–48.0.3; 49.0.0–49.0.1

## Identifiers

- GHSA-gqmc-89g8-p25r
- RUSTSEC-2026-0322

## Timeline

- 2026-10-02: disclosed

## References

- [https://crates.io/crates/wasmtime-wasi](https://crates.io/crates/wasmtime-wasi)
- [https://rustsec.org/advisories/RUSTSEC-2026-0322.html](https://rustsec.org/advisories/RUSTSEC-2026-0322.html)

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