High severity · published Jul 8, 2026
CVE-2026-59724
Socket.IO: Engine.IO WebTransport SID DoS
7.5
CVSS
0.6%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 49% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SO
socket.io · socketio
>= 6.5.0, < 6.6.7 · source: vendor
EN
Engine.io · Socket
6.5.0 before 6.6.7 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59724
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59724
Patch
https://github.com/socketio/socket.io/commit/1fa1f46cd420ac5b57bb4c04c959b58f3c79158c
Release Notes
https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7
Patch
https://github.com/socketio/socket.io/security/advisories/GHSA-gr94-w7qr-f4j3
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