---
id: "CVE-2026-115381"
kind: "vulnerability"
aliases: ["CVE-2026-115381"]
title: "Wasmtime: guest write-zeroes request exhausts host memory, causing denial of service"
severity: "medium"
cvss: 5.9
epss: 0.00212
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["runtime", "rust", "self-hosted", "wasi", "wasmtime"]
not_affected_if: ["stdout-stderr-configured", "trusted-guests-only"]
published_at: "2026-10-22T19:17:45+00:00"
first_seen_at: "2026-10-23T21:57:31+00:00"
updated_at: "2026-10-25T04:07:57+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115381", "first_seen_at": "2026-10-23T21:57:31+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-115381", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# Wasmtime: guest write-zeroes request exhausts host memory, causing denial of service

Wasmtime's WASIp2 write-zeroes method in SinkOutputStream allocates unbounded zero-filled buffers when stdout or stderr are not configured. A malicious WebAssembly guest can request huge writes and exhaust host memory, causing denial of service.

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

## How to check

- Run `wasmtime --version` and compare against the fixed releases.
- Check whether your host uses the wasmtime-wasi crate with WASIp2 and leaves stdout/stderr unconfigured.

## Fix

- Upgrade wasmtime to `36.0.17` on the 36 line, `48.0.4` on the 48 line, or `49.0.2` on the 49 line.

## Timeline

- 2026-10-23T21:57:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115381
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-115381

## From the sources

Wasmtime before 36.0.17, 37.0.0 before 48.0.4, and 49.0.0 before 49.0.2 contains an unbounded memory allocation in the wasmtime-wasi WASIp2 write-zeroes method of SinkOutputStream, the default stream used when stdout/stderr are not configured. A malicious WebAssembly guest can request huge zero-filled writes, exhausting host memory and causing denial of service.

---

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