---
id: CVE-2026-49860
title: 'Deno: WebSocket API sandbox bypass via missing post-DNS check'
summary: 'Deno: WebSocket API sandbox bypass via missing post-DNS check'
severity: medium
cvss: 5.2
cwe:
  - CWE-918
vendor: deno
product: deno
ecosystem: rust
affected:
  - deno <= 2.8.0
patched:
  - deno 2.8.1
published: '2026-06-16'
updated: '2026-06-16'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-83pc-3rw9-qpwj'
references:
  - url: 'https://github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj'
  - url: 'https://github.com/advisories/GHSA-83pc-3rw9-qpwj'
tags:
  - ghsa
  - rust
epss: 0.00141
epssPercentile: 0.02779
ingestedAt: '2026-06-29T14:31:47.714Z'
---

## Overview

## Summary

When a WebSocket connection was opened, Deno checked the destination hostname
against `--deny-net` rules but did not re-check the IP addresses that hostname
resolved to. An attacker-controlled script could use a specially crafted domain
name that passes the hostname check yet resolves to a denied IP, bypassing the
network restriction entirely.

## Impact

Code running under `--deny-net` could connect to hosts that the user intended
to block. In practice this means network isolation rules — for example,
blocking access to `localhost` or internal services — could be silently
circumvented by a malicious or compromised dependency.

`Deno.connect` and `fetch()` were not affected by this specific issue (a
companion advisory covers `fetch()`).

## Who is affected

Users who:

- run untrusted or third-party code with `deno run`, and
- rely on `--deny-net` to restrict which hosts that code can reach.

If you do not use `--deny-net`, or if you only run fully trusted code, you are
not affected.

## Workaround

No workaround is available short of upgrading. If upgrading immediately is not
possible, avoid granting `--allow-net` to untrusted code that also has
`--deny-net` restrictions you depend on for security.

## Affected packages

- `deno <= 2.8.0`

## Remediation

Upgrade to a patched release:

- `deno 2.8.1`