What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-20

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 products

• socketio engine.io: from 6.5.0 before 6.6.7 — fixed in 6.6.7

How to fix

Upgrade to a fixed version: socketio engine.io 6.6.7. Check the vendor advisory for mitigations.

References

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

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