---
id: "CVE-2026-115388"
kind: "vulnerability"
aliases: ["CVE-2026-115388"]
title: "Wasmtime: oversized HTTP body writes exhaust host memory from a guest"
severity: "medium"
cvss: 6.9
epss: 0.00112
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["runtime", "self-hosted", "wasi", "wasmtime", "webassembly"]
not_affected_if: ["no-wasi-http", "trusted-guests-only"]
published_at: "2026-10-22T19:17:46+00:00"
first_seen_at: "2026-10-23T21:57:31+00:00"
updated_at: "2026-10-25T03:38:45+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115388", "first_seen_at": "2026-10-23T21:57:31+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-115388", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# Wasmtime: oversized HTTP body writes exhaust host memory from a guest

Wasmtime's wasi-http implementation does not enforce the check-write limit for outgoing HTTP bodies under WASIp2, so oversized writes succeed instead of trapping. A malicious guest module can use this to hold host memory for the lifetime of its store 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 the affected ranges: before `36.0.16`, `37.0.0` through before `48.0.3`, and `49.0.0` through before `49.0.1`.
- Check whether your Cargo.lock pins `wasmtime-wasi-http` in those ranges.

## Fix

- Upgrade Wasmtime to `36.0.16`, `48.0.3`, or `49.0.1`, matching your release line.
- Rebuild and redeploy any host that embeds wasmtime-wasi-http.

## Timeline

- 2026-10-23T21:57:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115388
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-115388

## From the sources

wasmtime-wasi-http in Wasmtime before 36.0.16, 37.0.0 before 48.0.3, and 49.0.0 before 49.0.1 does not enforce the wasi:io/streams check-write allowance for WASIp2 outgoing HTTP bodies, so oversized writes succeed instead of trapping. A malicious guest can pass large buffers to write on outgoing-body resources, holding host allocations for the store's lifetime and 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_