High 7.5Published Oct 13, 2026

CVE-2026-102599Socket.IO: Engine.IO Protocol Revision Mismatch DoS

Updated under an hour ago (2026-10-19 06:30 UTC)

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It affects socketio socket.io. Add what you run to find out whether that includes you.

EPSS puts the chance of exploitation in the next 30 days at 0.58%, higher than 47% of scored CVEs.

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Every CVE for socketio socket.io

Exploited in the last 30 days

Socket.IO enables bidirectional and low-latency communication for every platform. From Engine.IO 6.6.0 until 6.6.10, a transport upgrade can independently derive an Engine.IO protocol revision from the upgrade request instead of enforcing the revision stored on the existing session. A malicious client can establish a valid session and send an upgrade request with a different or omitted EIO query parameter, attaching a transport with incompatible parser and heartbeat behavior. A crafted heartbeat packet can then trigger an uncaught exception and terminate the Node.js process, including when Engine.IO v3 compatibility is disabled because an omitted EIO value is interpreted as revision 3 on the affected path. This issue is fixed in Engine.IO 6.6.10.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-248
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.58% (percentile 47)
Assigned by: GitHub_M
NVD analysis: Awaiting Analysis
Record last updated: Oct 17, 2026
First seen by InfoSec Signals: Oct 13, 2026

Affected products

Affected products

socketio socket.io socketio:socket.io (from the name)	from 6.6.0, < 6.6.10	CNA record

References

https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gvx-refsource-confirm
https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729x-refsource-misc
https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.