CVE Intelligence
High

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

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.

Published Oct 13, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, GitHub Security Advisories, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.6% (30-day exploitation probability)+7
  • Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.58%
ahead of 47% of scored CVEs · Oct 15, 2026
Affects
Socketio
Socket.io and 1 more
CVSS base
7.5
High · 3 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Npm Engine.io: fixed in version 6.6.10 — github.com (GitHub Security Advisories)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Socketio Socket.io, Npm Engine.io).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Socketio Socket.io version >= 6.6.0, < 6.6.10 Vulnerable CVE Program (cve.org) e CISA ADP
Npm Engine.io ≥ 6.6.0 and < 6.6.10 Vulnerable GitHub Security Advisories

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
7.5 CVSS 3.1 High 3.9 3.6 security-advisories@github.com via NIST National Vulnerability Database
7.5 CVSS 3.1 High — — GitHub, Inc. via GitHub Security Advisories
7.5 CVSS 3.1 High — — GitHub_M via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-248

Other CVEs with this weakness →

EPSS over time FIRST

Oct 14, 2026 → Oct 15, 2026 · 2 reading(s) · max 0.58%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · socketio/socket.io
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Fix documented
    Oct 13, 2026 · GitHub Security Advisories
  • Affected products added · npm/engine.io
    Oct 13, 2026 · GitHub Security Advisories
  • Record published
    Oct 13, 2026
  • CVSS changed · 7.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Awaiting Analysis
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Oct 13, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

Elsewhere on this site

Socketio
every CVE for this vendor
CWE-248
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-102600 Socket.IO: Prototype Pollution via Unsafe Client Session Lookup 16d
  • CVE-2026-69185 Socket.IO: Zero-attachment Memory Exhaustion Aug 3, 2026
  • CVE-2026-59725 Socket.IO: Engine.IO Polling Transport Connection Exhaustion Jul 8, 2026
  • CVE-2026-59724 Socket.IO: Engine.IO WebTransport SID DoS Jul 8, 2026
  • CVE-2026-33151 socket.io allows an unbounded number of binary attachments Mar 20, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No CISA SSVC assessment.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-102599 is "Socket.IO: Engine.IO Protocol Revision Mismatch DoS", rated High. It affects Socket.io (Socketio); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.58% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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