Vulnerability-Lookup

CVE-2026-102599 (GCVE-0-2026-102599)

Vulnerability from cvelistv5 – Published: 2026-10-13 19:05 – Updated: 2026-10-13 19:05

Title

Socket.IO: Engine.IO Protocol Revision Mismatch DoS

Summary

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.

Severity

7.5 (High)


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

CWE

CWE-248 - Uncaught Exception

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7712 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/socketio/socket.io/security/ad…	x_refsource_CONFIRM
https://github.com/socketio/socket.io/commit/86db…	x_refsource_MISC
https://github.com/socketio/socket.io/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
socketio	socket.io	Affected: >= 6.6.0, < 6.6.10	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "socket.io",
          "vendor": "socketio",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 6.6.0, \u003c 6.6.10"
            }
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        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
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            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
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            "baseScore": 7.5,
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            "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"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-248",
              "description": "CWE-248: Uncaught Exception",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-13T19:05:10.870Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gv",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gv"
        },
        {
          "name": "https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729"
        },
        {
          "name": "https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10"
        }
      ],
      "source": {
        "advisory": "GHSA-2gc4-cqfq-p2gv",
        "discovery": "UNKNOWN"
      },
      "title": "Socket.IO: Engine.IO Protocol Revision Mismatch DoS"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-102599",
    "datePublished": "2026-10-13T19:05:10.870Z",
    "dateReserved": "2026-09-29T14:18:02.920Z",
    "dateUpdated": "2026-10-13T19:05:10.870Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
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      "date": "2026-10-15",
      "epss": "0.00583",
      "percentile": "0.46684"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "socket.io",
                "vendor": "socketio",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003e= 6.6.0, \u003c 6.6.10"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "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."
          }
        ],
        "id": "CVE-2026-102599",
        "lastModified": "2026-10-13T19:25:38.150",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "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"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 3.6,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-10-13T19:17:49.037",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gv"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-248"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-10-15T21:29:20+00:00",
      "cve": "CVE-2026-102599",
      "id": "CVE-2026-102599",
      "initial_release_date": "2026-10-13T19:05:10.870000+00:00",
      "product_status:known_not_affected": "10",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "engine.io: engine.io: Denial of Service via protocol revision mismatch during transport upgrade",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-102599.json",
      "version": "3"
    }
  }
}

FKIE_CVE-2026-102599

Vulnerability from fkie_nvd - Published: 2026-10-13 19:17 - Updated: 2026-10-13 19:25

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729
	security-advisories@github.com	https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10
	security-advisories@github.com	https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gv

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "socket.io",
          "vendor": "socketio",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 6.6.0, \u003c 6.6.10"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2026-102599",
  "lastModified": "2026-10-13T19:25:38.150",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "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"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-10-13T19:17:49.037",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gv"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-248"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-2GC4-CQFQ-P2GV

Vulnerability from github – Published: 2026-09-29 23:44 – Updated: 2026-09-29 23:44

Summary

Socket.IO: Engine.IO Protocol Revision Mismatch DoS

Details

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 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.

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": "6.6.0"
            },
            {
              "fixed": "6.6.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-102599"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-248"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-29T23:44:33Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Impact\n\nA denial-of-service vulnerability exists in Engine.IO / Socket.IO servers that allow transport upgrades.\n\nThe 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.\n\nA 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.\n\nServers 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.\n\nThe impact is **denial of service** through process crash.\n\nAffected versions:\n\n- `engine.io \u003e= 6.6.0, \u003c 6.6.10`\n\n## Patches\n\nThe issue was fixed in:\n\n- **engine.io 6.6.10**\n\nUsers should upgrade to `engine.io@6.6.10` or later.\n\nIf using Socket.IO packages that depend on Engine.IO, users should update to a Socket.IO release that includes the patched Engine.IO version.\n\n### Workarounds\n\nIf upgrading is not immediately possible, users can reduce exposure by disabling transport upgrades:\n\n```javascript\nconst io = new Server(httpServer, {\n  allowUpgrades: false\n});\n```\n\nor by allowing only a single transport, for example WebSocket only:\n\n```javascript\nconst io = new Server(httpServer, {\n  transports: [\"websocket\"]\n});\n```\n\nThese mitigations avoid the vulnerable upgrade path, but they may affect client compatibility and connection behavior.\n\nAs 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\u2019s negotiated protocol.\n\nUpgrading remains the recommended fix.",
  "id": "GHSA-2gc4-cqfq-p2gv",
  "modified": "2026-09-29T23:44:33Z",
  "published": "2026-09-29T23:44:33Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/socketio/socket.io/security/advisories/GHSA-2gc4-cqfq-p2gv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/socketio/socket.io/commit/86db1fc3db2cd315a065d64c4e48918ccf9b4729"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/socketio/socket.io"
    },
    {
      "type": "WEB",
      "url": "https://github.com/socketio/socket.io/releases/tag/engine.io@6.6.10"
    }
  ],
  "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 Protocol Revision Mismatch DoS"
}

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.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

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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.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-102599 (GCVE-0-2026-102599)

FKIE_CVE-2026-102599

GHSA-2GC4-CQFQ-P2GV

Impact

Patches

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Related by attack behaviour