---
id: "CVE-2026-126409"
page: "https://infrastack.ai/live/CVE-2026-126409"
kind: "vulnerability"
aliases: ["CVE-2026-126409"]
title: "Wasmtime: cross-engine supertype check missing lets embedders corrupt GC heap"
severity: "low"
cvss: 2.0
epss: null
exploited: false
status: "open"
category: "runtime"
products: [{"name": "wasmtime", "fixed": [], "affected": "", "ecosystem": "cargo"}]
ecosystems: ["cargo"]
tags: ["runtime", "rust", "wasmtime", "webassembly"]
not_affected_if: ["guest-only-wasm", "single-engine", "wasmtime-outside-affected-ranges"]
published_at: "2026-11-13T10:17:46+00:00"
first_seen_at: "2026-11-13T10:47:20+00:00"
updated_at: "2026-11-13T10:59:04+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126409", "first_seen_at": "2026-11-13T10:47:20+00:00"}]
exploit_sources: []
---

# Wasmtime: cross-engine supertype check missing lets embedders corrupt GC heap

Link for people: https://infrastack.ai/live/CVE-2026-126409 (this .md is for agents)

Wasmtime's StructType::with_finality_and_supertype does not check that a supertype belongs to the same Engine, so mixing engines can cause runtime panics or GC heap corruption. The result is denial of service; guest WebAssembly code cannot trigger it.

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

## Affected

- cargo:wasmtime affected range not listed fixed no fixed version listed

## How to check

- Check the Wasmtime version in your build: `wasmtime --version` or the wasmtime crate version in `Cargo.lock`.
- Look for code that creates more than one Engine and builds GC struct types with supertypes (StructType::with_finality_and_supertype).

## Fix

- Wasmtime `48.0.8`
- Wasmtime `49.0.5`
- Wasmtime `50.0.1`

## Timeline

- 2026-11-13T10:47:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126409

## Documents

- [advisory] Vendor advisory: github.com https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-qw58-7h65-crq2
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/wasmtime-47.0.0-before-48.0.8-cross-engine-type-confusion-via-structtype-supertype

## 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 a cross-engine type confusion vulnerability because StructType::with_finality_and_supertype does not validate that the supplied supertype belongs to the same Engine. Embedders using multiple engines that create a GC struct type with another engine's supertype can trigger runtime panics or GC heap corruption, causing denial of service; guest WebAssembly cannot trigger it.

---

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