Vulnerability in engine.io (CVE-2026-102599)
Summary
Vulnerability in engine.io (CVE-2026-102599). Risk of unauthorized operations or information disclosure. Exploitable via EIO. Mitigation: upgrade to 6.6.10 or later.
Original description
The description as published by the source.
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 engine.io@6.6.10 or later.
If using Socket.IO packages that depend on Engine.IO, users should update to a Socket.IO rel…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-102599 has been found in engine.io.
Attackers can target a specific entry point like EIO over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade engine.io to 6.6.10 or later.
If unsure, ask your IT team or search "engine.io CVE-2026-102599" on the vendor's site.
CVE-2026-102599 (engine.io) — CWE-248 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: EIO / sid
Patched: 6.6.10 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-248) exists in engine.io. Attackers reach the vulnerable code path via EIO without authentication.
Check the vendor advisory for the affected versions of engine.io. Attack surface: EIO / sid.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 6.6.10.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'engine.io' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'engine.io' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
engine.ioを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade engine.io to 6.6.10ステージング環境で 6.6.10 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- REDHAT Red Hat
- web security-advisories@github.com
- web security-advisories@github.com
- web security-advisories@github.com
- web github.com