Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-59724Socket.IO: Engine.IO WebTransport SID DoS

High 7.5

In plain English

A high-severity improper input validation in socket.io from socketio. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.6%top 50.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Socket.IO enables bidirectional and low-latency communication for every platform. From 6.5.0 before 6.6.7, Engine.IO servers with WebTransport enabled can resolve a crafted session ID such as __proto__ through an inherited property of the clients object during WebTransport upgrade handling, causing a TypeError and denial of service. This issue is fixed in version 6.6.7.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	engine.io	6.6.7	GHSA-gr94-w7qr-f4j3

Affected products (as reported)

Vendor	Product	Versions
socketio	socket.io	>= 6.5.0, < 6.6.7

Weakness: CWE-20 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/socketio/socket.io/security/advisories/GHSA-gr94-w7qr-f4j3 x_refsource_CONFIRM
https://github.com/socketio/socket.io/commit/1fa1f46cd420ac5b57bb4c04c959b58f3c79158c x_refsource_MISC
https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7 x_refsource_MISC