Denial of Service Vulnerability in Engine.IO Servers by Socket.IO
CVE-2026-59724

7.5HIGH

Key Information:

Vendor

Socketio

Status
Socket.io
Vendor
CVE Published:
8 July 2026

What is CVE-2026-59724?

Socket.IO enables seamless bidirectional communication for various platforms. A vulnerability in Engine.IO versions 6.5.0 to 6.6.6 with WebTransport enabled allows the exploitation of crafted session IDs via inherited properties in the client object during WebTransport upgrade handling. This can trigger a TypeError, leading to a denial of service condition. Users are encouraged to upgrade to version 6.6.7, where this issue has been resolved.

Affected Version(s)

socket.io >= 6.5.0, < 6.6.7

References

https://github.com/socketio/socket.io/security/advisories...
x_refsource_CONFIRM
https://github.com/socketio/socket.io/commit/1fa1f46cd420...
x_refsource_MISC
https://github.com/socketio/socket.io/releases/tag/engine...
x_refsource_MISC

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.