---
id: "CVE-2026-126410"
page: "https://infrastack.ai/live/CVE-2026-126410"
kind: "vulnerability"
aliases: ["CVE-2026-126410"]
title: "Wasmtime WASI: UDP socket race lets guests send to blocked addresses"
severity: "medium"
cvss: 6.4
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "rust", "wasi", "wasmtime", "webassembly"]
not_affected_if: ["no-untrusted-guests", "wasip3-sockets-unused"]
published_at: "2026-11-13T10:17:46+00:00"
first_seen_at: "2026-11-13T10:47:20+00:00"
updated_at: "2026-11-13T10:55:03+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126410", "first_seen_at": "2026-11-13T10:47:20+00:00"}]
exploit_sources: []
---

# Wasmtime WASI: UDP socket race lets guests send to blocked addresses

Link for people: https://infrastack.ai/live/CVE-2026-126410 (this .md is for agents)

A time-of-check/time-of-use race in the wasip3 wasi:sockets UDP implementation of wasmtime-wasi lets a malicious guest bypass send address restrictions. An attacker-controlled guest can deliver datagrams to addresses the policy only allows for receiving.

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

## How to check

- Check the `wasmtime-wasi` version in `Cargo.lock` or your dependency tree; affected are 48.0.0 to before 48.0.8, 49.0.0 to before 49.0.5, and 50.0.0 to before 50.0.1.
- Check whether the application uses the wasip3 `wasi:sockets` UDP interface for untrusted guests.

## Fix

- `wasmtime-wasi` `48.0.8`
- `wasmtime-wasi` `49.0.5`
- `wasmtime-wasi` `50.0.1`

## Timeline

- 2026-11-13T10:47:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126410

## Documents

- [advisory] Vendor advisory: github.com https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hmmr-87qq-258j
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/wasmtime-48.0.0-before-48.0.8-toctou-udp-send-policy-bypass-via-wasip3-sockets

## From the sources

Wasmtime's wasmtime-wasi crate 48.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains a time-of-check/time-of-use race in the wasip3 wasi:sockets udp-socket host implementation that lets guests bypass socket_addr_check send restrictions. A malicious guest can race udp-socket.send against udp-socket.connect to deliver attacker-controlled datagrams to addresses the policy permits only for receiving.

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