---
id: "CVE-2026-115389"
kind: "vulnerability"
aliases: ["CVE-2026-115389"]
title: "Wasmtime: crafted guest return values exhaust host memory, denial of service"
severity: "low"
cvss: 2.3
epss: 0.00152
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["plugin-systems", "runtime", "rust", "self-hosted", "wasmtime"]
not_affected_if: ["trusted-guest-only", "typed-api-only", "wasmtime-not-embedded"]
published_at: "2026-10-22T19:17:46+00:00"
first_seen_at: "2026-10-23T21:57:31+00:00"
updated_at: "2026-10-25T04:49:41+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115389", "first_seen_at": "2026-10-23T21:57:31+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-115389", "first_seen_at": "2026-10-24T07:15:51+00:00"}]
---

# Wasmtime: crafted guest return values exhaust host memory, denial of service

Wasmtime's dynamically-typed Val API does not count host memory allocated while lifting guest return values, so it bypasses the hostcall fuel limit. A malicious WebAssembly guest can make the host allocate about 100 times more memory than tracked, causing denial of service.

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

## How to check

- Run `wasmtime --version` on the host or check the pinned wasmtime crate version in `Cargo.lock`
- Search the codebase for uses of the dynamically-typed `Val` API when running untrusted guest modules
- unknown for anything beyond this

## Fix

- Upgrade wasmtime to `36.0.16` on the 36.x line, `48.0.3` on the 48.x line (37.0.0 and later within that range), or `49.0.1` on the 49.x line
- unknown for any workaround beyond upgrading

## Timeline

- 2026-10-23T21:57:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115389
- 2026-10-24T07:15:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-115389

## From the sources

Wasmtime before 36.0.16, 37.0.0 before 48.0.3, and 49.0.0 before 49.0.1 does not adequately account for host allocations when lifting guest values through the dynamically-typed Val API, bypassing the hostcall fuel limit. A malicious WebAssembly guest can return crafted values that allocate at least ~100x more host memory than tracked, causing denial of service.

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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_