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CVE-2026-59725 high CVSS 7.5

Vulnerability in engine.io (CVE-2026-59725)

Summary

Vulnerability in engine.io (CVE-2026-59725). Risk of unauthorized operations or information disclosure. Exploitable via POST. Mitigation: upgrade to 6.6.7 or later.

Original description

The description as published by the source.

Impact

An unauthenticated remote attacker can cause a denial of service in affected versions of engine.io by opening Engine.IO polling sessions and sending an invalid binary POST request with:

Content-Type: application/octet-stream

against an Engine.IO protocol v4 polling transport.

In the vulnerable code path, the server reports a transport error but does not properly close the HTTP response associated with the malformed request. As a result, the underlying HTTP connection may remain open, consuming one server-side socket/resource per crafted request.

An attacker can repeat this with many sessions to exhaust available HTTP connections, sockets, file descriptors, or related server resources, potentially preventing legitimate clients from connecting.

Patches

The issue was fixed in:

  • engine.io 6.6.7

The fix ensures that invalid binary polling POST requests are explicitly rejected with an HTTP response and closed properly.

Users should upgrade to:

npm install engine.io@^6.6.7

or a later fixed version.

If using Socket.IO through the monorepo/packages, update to a Socket.IO release that depends on a fixed engine.io version.

Workarounds

If upgrading immediately is not possible, possible mitigations include:

  • Block or reject polling POST requests with Content-Type: application/octet-stream for Engine.IO protocol v4 at a reverse proxy, load balancer, WAF, or application middleware.
  • Disable HTTP long-polling if your…

Source: NIST National Vulnerability Database 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-2026-59725 has been found in engine.io.
Attackers can target a specific entry point like POST 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 6.6.7 or later.
If unsure, ask your IT team or search "engine.io CVE-2026-59725" on the vendor's site.

CVE-2026-59725 (engine.io) — CWE-404 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: POST / engine.io
Patched: 6.6.7 — 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.

❓ What is the problem

A vulnerability (CWE-404) exists in engine.io. Attackers reach the vulnerable code path via POST without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of engine.io. Attack surface: POST / engine.io.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 6.6.7.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

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

  1. 1
    Identify 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。

  2. 2
    Apply patch patch 
    Upgrade engine.io to 6.6.7

    ステージング環境で 6.6.7 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。

  3. 3
    Post-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

npm engine.io
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6.7"}]}]

References

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