# CVE-2026-115391: Wasmtime WASIp3 uncontrolled resource allocation in streams

Source: https://junglewise.ai/threats/cve-2026-115391-wasmtime-46-0-0-before-46-0-3-and-47-0-0-before-47-0-4-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-2026-115391 · Severity: medium · CVSS 5.8 · Published 2026-10-22

Wasmtime is a WebAssembly runtime that executes untrusted guest code. The WASIp3 implementation fails to limit the size of buffers that guest code can write to file or HTTP streams on the host system. A malicious WebAssembly program can exhaust the host's memory by instructing the runtime to buffer arbitrarily large amounts of data, causing denial of service.

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-2026-115391 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115391 being exploited in the wild.

**How severe is CVE-2026-115391?** Medium severity, with a CVSS score of 5.8, published 22 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime 46.0.0 before 46.0.3, 47.0.0 before 47.0.4.

**Is there a fix for CVE-2026-115391?** Yes: fixed in Wasmtime 46.0.3, 47.0.4. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-115391 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-115391?** 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 46.0.3, 47.0.4

## Technical details

Wasmtime's WASIp3 file and HTTP stream write operations copy guest-specified buffer sizes onto the host heap without enforcing limits, allowing guest code to trigger unbounded memory allocation. The vulnerability requires the attacker to control the guest WebAssembly code and have WASIp3 enabled (default in 46.0.0+). This causes host memory exhaustion leading to availability impact.

## Affected products

- Bytecode Alliance Wasmtime 46.0.0 before 46.0.3, 47.0.0 before 47.0.4

## Timeline

- 2026-08-20: disclosed
- 2026-10-22: advisory

## References

- [https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-x84v-gj2h-g759](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-x84v-gj2h-g759)
- [https://www.vulncheck.com/advisories/wasmtime-46.0.0-before-46.0.3-and-47.0.0-before-47.0.4-unbounded-heap-allocation-via-wasip3-streams](https://www.vulncheck.com/advisories/wasmtime-46.0.0-before-46.0.3-and-47.0.0-before-47.0.4-unbounded-heap-allocation-via-wasip3-streams)

## 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)