---
id: CVE-2026-59725
title: >-
  Socket.IO enables bidirectional and low-latency communication for every
  platform
summary: >-
  Socket.IO enables bidirectional and low-latency communication for every
  platform. From 4.1.0 before 6.6.7, Engine.IO protocol v4 polling transport
  does not properly close the HTTP response for invalid binary POST requests
  with Content-Ty…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-404
vendor: socket
product: engine.io
affected:
  - 'engine.io >= 4.1.0, < 6.6.7'
patched:
  - engine.io 6.6.7
published: '2026-07-08'
updated: '2026-07-13'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-59725'
references:
  - url: >-
      https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671
    label: security-advisories@github.com
  - url: 'https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7'
    label: security-advisories@github.com
  - url: >-
      https://github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7x
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00636
epssPercentile: 0.48298
ingestedAt: '2026-07-13T15:27:34.133Z'
---

## Overview

Socket.IO enables bidirectional and low-latency communication for every platform. From 4.1.0 before 6.6.7, Engine.IO protocol v4 polling transport does not properly close the HTTP response for invalid binary POST requests with Content-Type: application/octet-stream, allowing an unauthenticated attacker to exhaust server-side connections and sockets. This issue is fixed in version 6.6.7.

## Affected

- `engine.io >= 4.1.0, < 6.6.7`

## Remediation

Upgrade past the affected range:

- `engine.io 6.6.7`