Vulnerability-Lookup

GHSA-R635-G3XR-VW7X

Vulnerability from github – Published: 2026-07-20 21:49 – Updated: 2026-07-20 21:49

Summary

Socket.IO: Engine.IO Polling Transport Connection Exhaustion

Details

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 deployment can use WebSocket-only transport.
Enforce strict request/connection timeouts at the HTTP server, reverse proxy, or load balancer.
Apply per-IP rate limits and connection limits for Engine.IO endpoints.
Restrict access to the Socket.IO/Engine.IO endpoint where feasible.

Example Socket.IO configuration to disable polling, if compatible with your clients:

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

References

Fix commit: https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671
engine.io changelog entry for 6.6.7: https://github.com/socketio/socket.io/blob/main/packages/engine.io/CHANGELOG.md#667-2026-04-27
socket.io repository: https://github.com/socketio/socket.io
engine.io package: https://www.npmjs.com/package/engine.io

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "engine.io"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.1.0"
            },
            {
              "fixed": "6.6.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59725"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-404"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-20T21:49:54Z",
    "nvd_published_at": "2026-07-08T16:16:33Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nAn 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:\n\n```\nContent-Type: application/octet-stream\n```\n\n\nagainst an Engine.IO protocol v4 polling transport.\n\nIn 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.\n\nAn 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.\n\n### Patches\n\nThe issue was fixed in:\n\n- **engine.io `6.6.7`**\n\nThe fix ensures that invalid binary polling `POST` requests are explicitly rejected with an HTTP response and closed properly.\n\nUsers should upgrade to:\n\n```sh\nnpm install engine.io@^6.6.7\n```\n\nor a later fixed version.\n\nIf using Socket.IO through the monorepo/packages, update to a Socket.IO release that depends on a fixed `engine.io` version.\n\n### Workarounds\n\nIf upgrading immediately is not possible, possible mitigations include:\n\n- 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.\n- Disable HTTP long-polling if your deployment can use WebSocket-only transport.\n- Enforce strict request/connection timeouts at the HTTP server, reverse proxy, or load balancer.\n- Apply per-IP rate limits and connection limits for Engine.IO endpoints.\n- Restrict access to the Socket.IO/Engine.IO endpoint where feasible.\n\nExample Socket.IO configuration to disable polling, if compatible with your clients:\n\n```js\nconst io = new Server(httpServer, {\n  transports: [\"websocket\"],\n});\n```\n\n## References\n\n- Fix commit: https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671\n- engine.io changelog entry for `6.6.7`: https://github.com/socketio/socket.io/blob/main/packages/engine.io/CHANGELOG.md#667-2026-04-27\n- socket.io repository: https://github.com/socketio/socket.io\n- engine.io package: https://www.npmjs.com/package/engine.io",
  "id": "GHSA-r635-g3xr-vw7x",
  "modified": "2026-07-20T21:49:54Z",
  "published": "2026-07-20T21:49:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7x"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-59725"
    },
    {
      "type": "WEB",
      "url": "https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/socketio/socket.io"
    },
    {
      "type": "WEB",
      "url": "https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.7"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Socket.IO: Engine.IO Polling Transport Connection Exhaustion"
}

CVE-2026-59725 (GCVE-0-2026-59725)

Vulnerability from cvelistv5 – Published: 2026-07-08 15:37 – Updated: 2026-07-08 17:00

Title

Socket.IO: Engine.IO Polling Transport Connection Exhaustion

Summary

Socket.IO enables bidirectional and low-latency communication for every platform. From 4.1.0 before 6.6.7, Engine.IO protocol v4 polling transport does not properly close the HTTP response for invalid binary POST requests with Content-Type: application/octet-stream, allowing an unauthenticated attacker to exhaust server-side connections and sockets. This issue is fixed in version 6.6.7.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-404 - Improper Resource Shutdown or Release

Assigner

GitHub_M

References

3 references

URL	Tags
https://github.com/socketio/socket.io/security/ad…	x_refsource_CONFIRM
https://github.com/socketio/socket.io/commit/fc11…	x_refsource_MISC
https://github.com/socketio/socket.io/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
socketio	socket.io	Affected: >= 4.1.0, < 6.6.7

Show details on NVD website

JSON

To clipboard

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  "containers": {
    "adp": [
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        "metrics": [
          {
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                "id": "CVE-2026-59725",
                "options": [
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                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-08T16:50:45.800976Z",
                "version": "2.0.3"
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          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
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          "descriptions": [
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      "providerMetadata": {
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      },
      "references": [
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          ],
          "url": "https://github.com/socketio/socket.io/security/advisories/GHSA-r635-g3xr-vw7x"
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        {
          "name": "https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671",
          "tags": [
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          "url": "https://github.com/socketio/socket.io/commit/fc11285e14964c2132d122164bf130c355f60671"
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      "source": {
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    "dateReserved": "2026-07-06T15:34:16.916Z",
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    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

GHSA-R635-G3XR-VW7X

Impact

Patches

Workarounds

References

CVE-2026-59725 (GCVE-0-2026-59725)

Tags

Sightings

Nomenclature