# CVE-2026-115391: Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 Unbounded Heap Allocation via WASIp3 Streams


- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 22 Oct 2026
- **Updated:** 22 Oct 2026
- **Also known as:** GHSA-6862-f859-6m9r, GHSA-x84v-gj2h-g759, RUSTSEC-2026-0268, UBUNTU-CVE-2026-115391

## What is CVE-2026-115391?

CVE-2026-115391 is a medium-severity vulnerability in bytecodealliance wasmtime, published on 22 Oct 2026. 

### Official description

Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 contains an uncontrolled resource allocation vulnerability in its WASIp3 implementation that buffers guest-specified-length writes on the host without limit. Malicious guests can offer large buffers to WASIp3 file or HTTP write streams, causing the host to copy and buffer all bytes, bounded only by guest linear memory, exhausting host memory.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-115391?

1 open source package ship an affected version, including wasmtime.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `wasmtime` | crates.io | From 46.0.0 | 46.0.3, 47.0.4 |

## How do I fix CVE-2026-115391?

Upgrade wasmtime to a fixed version for your release line: 46.0.3 or 47.0.4.

## Is CVE-2026-115391 being exploited?

There is no known exploitation of CVE-2026-115391 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-115391 and fix it if it is affected.

What it is: CVE-2026-115391 is a medium-severity vulnerability in bytecodealliance wasmtime, published on 22 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-115391 in the wild and no public exploit code.

Affected packages and fixed versions:
- wasmtime (crates.io): affected from 46.0.0; fixed in 46.0.3, 47.0.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-115391/ (Markdown: https://insights.sbomify.com/CVE-2026-115391/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-115391
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-115391
- OSV: https://osv.dev/vulnerability/CVE-2026-115391

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-115391/
Summaries are generated and may contain mistakes; the official description above is the record.