CVE-2026-102599

HIGHPre-NVD 7.57.5
EchelonGraph scoreLOW confidence

This high-severity CVE scores 7.5 under the CNA's CVSS (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: cna:github_m
7.5EG
EchelonGraph verdictPlan mitigationSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: —CVSS: 7.5Exploit: None knownExposed services: Not assessed

No fix is confirmed yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for the fix.

Socket.IO: Engine.IO Protocol Revision Mismatch DoS

Impact

A denial-of-service vulnerability exists in Engine.IO / Socket.IO servers that allow transport upgrades.

The Engine.IO protocol revision is negotiated during the initial handshake and stored on the session, but a newly-created transport, including a WebSocket upgrade transport, could independently derive a different protocol revision from the upgrade request query parameters. The server did not verify that the protocol revision of an upgrade request matched the protocol revision of the existing session.

A malicious client could exploit this mismatch by establishing a valid Engine.IO session and then sending an upgrade request with a different, or omitted, EIO query parameter. This could cause the server to attach a transport using a parser and heartbeat behavior inconsistent with the session. Under some conditions, a crafted heartbeat packet could trigger an uncaught exception and terminate the Node.js process.

Servers using the default Engine.IO v4 protocol are impacted. The issue can be triggered even when Engine.IO v3 compatibility is disabled, because an omitted EIO parameter is interpreted as protocol v3 on the affected transport path.

The impact is denial of service through process crash.

Affected versions:

  • engine.io >= 6.6.0, < 6.6.10

Patches

The issue was fixed in:

  • engine.io 6.6.10

Users should upgrade to [email protected] or later.

If using Socket.IO packages that depend on Engine.IO, users should update to a Socket.IO release that includes the patched Engine.IO version.

Workarounds

If upgrading is not immediately possible, users can reduce exposure by disabling transport upgrades:

const io = new Server(httpServer, {
  allowUpgrades: false
});

or by allowing only a single transport, for example WebSocket only:

const io = new Server(httpServer, {
  transports: ["websocket"]
});

These mitigations avoid the vulnerable upgrade path, but they may affect client compatibility and connection behavior.

As an additional temporary mitigation, deployments may reject Engine.IO requests for an existing sid when the EIO query parameter is missing or does not match the protocol revision used during the initial handshake. This is best done at the application proxy or middleware layer only if the deployment can reliably track the session’s negotiated protocol.

Upgrading remains the recommended fix.

CVSS v3
7.5
EG Score
7.5HIGHlow confidence
EG Risk
38
EG Risk 38/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity75% × 45%
Exploitation0% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track or Attend at high (mission-essential systems).
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
EPSS PROB
—
EPSS %ILE
—
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track or Attend at high (mission-essential systems).

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

September 29, 2026

Last Modified

September 29, 2026

Vendor Advisories for CVE-2026-102599(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFix by version rangeDependents
engine.io—
  • 6.6.0 up to 6.6.10: fixed in 6.6.10
—

Data Freshness Timeline

(refreshed 1× in last 7d / 1× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-30 00:11 UTCEG score recompute

Related CVEs(same product)

Frequently asked(4)

What is CVE-2026-102599?
CVE-2026-102599 is a high vulnerability published on September 29, 2026. Socket.IO: Engine.IO Protocol Revision Mismatch DoS Impact A denial-of-service vulnerability exists in Engine.IO / Socket.IO servers that allow transport upgrades. The Engine.IO protocol revision is negotiated during the initial handshake and stored on the session, but a newly-created transport,…
When was CVE-2026-102599 disclosed?
CVE-2026-102599 was first published on September 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
What is the CVSS score of CVE-2026-102599?
CVE-2026-102599 has a CVSS base score of 7.5 (the CNA's own assessment, by github_m; NVD's own analysis pending). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-102599?
No fix for CVE-2026-102599 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The vendor advisories EchelonGraph has for CVE-2026-102599 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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