---
id: "CVE-2026-115391"
kind: "vulnerability"
aliases: ["CVE-2026-115391"]
title: "Wasmtime: unbounded WASIp3 write buffering lets a guest exhaust host memory"
severity: "medium"
cvss: 6.9
epss: 0.00172
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["runtime", "self-hosted", "wasm", "wasmtime", "webassembly"]
not_affected_if: ["patched-version", "pre-wasip3-usage", "trusted-guests-only"]
published_at: "2026-10-22T19:17:46+00:00"
first_seen_at: "2026-10-23T21:57:31+00:00"
updated_at: "2026-10-25T03:38:41+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115391", "first_seen_at": "2026-10-23T21:57:31+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-115391", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# Wasmtime: unbounded WASIp3 write buffering lets a guest exhaust host memory

Wasmtime's WASIp3 implementation copies and buffers every byte of guest-specified-length writes on the host with no limit. A malicious guest module can offer large buffers to file or HTTP write streams and exhaust the host's memory.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `wasmtime --version` and compare against `46.0.3` and `47.0.4`
- Check Cargo.lock or go.mod for the `wasmtime` crate or library version in projects that embed it

## Fix

- Upgrade Wasmtime to `46.0.3` (46.x line) or `47.0.4` (47.x line)

## Timeline

- 2026-10-23T21:57:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115391
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-115391

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_