---
id: "CVE-2026-119136"
kind: "vulnerability"
aliases: ["CVE-2026-119136"]
title: "Wasmtime: mixing sync and async WebAssembly calls can panic or misuse host data"
severity: "medium"
cvss: 5.9
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["plugin-hosts", "runtime", "rust", "wasmtime", "webassembly"]
not_affected_if: ["default-config", "single-calling-style"]
published_at: "2026-10-29T16:18:06+00:00"
first_seen_at: "2026-10-29T16:25:58+00:00"
updated_at: "2026-10-29T16:31:40+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-119136", "first_seen_at": "2026-10-29T16:25:58+00:00"}]
---

# Wasmtime: mixing sync and async WebAssembly calls can panic or misuse host data

Wasmtime, a WebAssembly runtime, does not fully check calls that mix async-style and sync-style WebAssembly entry points when a host function re-enters WebAssembly. An attacker who can drive such an embedder can trigger runtime panics or move non-thread-safe host variables across threads.

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

## How to check

- Run `wasmtime --version` or check the `wasmtime` crate version in `Cargo.lock`
- Look for embedders that call sync WebAssembly APIs from host functions invoked asynchronously
- Check whether untrusted input reaches a Wasmtime Store through that path

## Fix

- Wasmtime `42.0.0` before `48.0.6` and `49.0.0` before `49.0.3` are affected; move to `48.0.6` or `49.0.3` or later on the matching release line

## Timeline

- 2026-10-29T16:25:58+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-119136

## From the sources

Wasmtime 42.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains insufficient checks in Store when mixing async-style and sync-style WebAssembly calls. Embedders re-entering WebAssembly via sync APIs from host functions called asynchronously can trigger runtime panics or unsound cross-thread movement of !Send host variables.

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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_