---
id: "CVE-2026-126408"
page: "https://infrastack.ai/live/CVE-2026-126408"
kind: "vulnerability"
aliases: ["CVE-2026-126408"]
title: "Wasmtime: type-check gap lets a guest module crash the host"
severity: "low"
cvss: 1.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "rust", "wasmtime", "webassembly"]
not_affected_if: ["no-embedding", "trusted-modules-only"]
published_at: "2026-11-13T10:17:45+00:00"
first_seen_at: "2026-11-13T10:47:20+00:00"
updated_at: "2026-11-13T10:59:05+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126408", "first_seen_at": "2026-11-13T10:47:20+00:00"}]
exploit_sources: []
---

# Wasmtime: type-check gap lets a guest module crash the host

Link for people: https://infrastack.ai/live/CVE-2026-126408 (this .md is for agents)

Wasmtime's TypedFunc embedder API fails to type-check I31 and Option<NoneRef> parameters and results, reaching an unreachable!() path. A malicious WebAssembly guest module can make the host embedding panic, causing denial of service.

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

## How to check

- Check the Wasmtime version in your dependency manifest (for example `Cargo.lock`) and compare it with the fixed versions below.
- Look for embedders that load untrusted guest modules and call functions through the TypedFunc API with anyref-hierarchy types.

## Fix

- `48.0.8` for the 47.x and 48.x line before the fix
- `49.0.5` for the 49.x line
- `50.0.1` for the 50.x line

## Timeline

- 2026-11-13T10:47:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126408

## Documents

- [advisory] Vendor advisory: github.com https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-3982-jqvv-277m
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/wasmtime-47.0.0-before-48.0.8-denial-of-service-via-typedfunc-type-check-panic

## From the sources

Wasmtime 47.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains an insufficient type-check in the TypedFunc embedder API for I31, Option<I31>, and Option<NoneRef> parameter or result types, reaching an unreachable!() path. A malicious guest module exporting a function that uses another anyref-hierarchy type can panic the host embedding, causing denial of service.

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