Input validation error in socket.io - #VU149945
Published: September 15, 2026
Vulnerability identifier: #VU149945
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper validation of protocol revision consistency in the Engine.IO transport upgrade handling when processing an upgrade request for an existing Engine.IO session. A remote attacker can establish a valid session and send an upgrade request with a different or omitted EIO query parameter to cause a denial of service.
Only servers that allow transport upgrades are affected; a crafted heartbeat packet can trigger an uncaught exception that terminates the Node.js process.
Affected software
socket.io
Remediation
Install security update from vendor's website.
socket.io - update to 6.6.10