Vulnerability-Lookup

CVE-2026-42236 (GCVE-0-2026-42236)

Vulnerability from cvelistv5 – Published: 2026-05-04 18:38 – Updated: 2026-05-04 19:59

Title

n8n: Unauthenticated Denial of Service via MCP Client Registration

Summary

n8n is an open source workflow automation platform. Prior to versions 1.123.32, 2.17.4, and 2.18.1, the MCP OAuth client registration endpoint accepted unauthenticated requests and stored client data without adequate resource controls. An unauthenticated remote attacker could exhaust server memory resources by sending large registration payloads, rendering the n8n instance unavailable. The MCP enable/disable toggle gates MCP access but did not restrict client registrations, meaning the endpoint is reachable regardless of whether MCP access is enabled on the instance. This issue has been patched in versions 1.123.32, 2.17.4, and 2.18.1.

Severity ?

8.7 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CWE

CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

GitHub_M

References

URL

Tags

https://github.com/n8n-io/n8n/security/advisories…

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	n8n-io	n8n	Affected: < 1.123.32 Affected: >= 2.17.0, < 2.17.4 Affected: >= 2.18.0, < 2.18.1

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-42236

Vulnerability from fkie_nvd - Published: 2026-05-04 19:16 - Updated: 2026-05-06 17:16

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/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6	Vendor Advisory

Impacted products

Vendor	Product	Version
n8n	n8n	*
n8n	n8n	*
n8n	n8n	2.18.0

JSON

To clipboard

{
  "configurations": [
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              "criteria": "cpe:2.3:a:n8n:n8n:*:*:*:*:enterprise:node.js:*:*",
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              "versionEndExcluding": "1.123.32",
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    }
  ],
  "id": "CVE-2026-42236",
  "lastModified": "2026-05-06T17:16:02.340",
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GHSA-49M9-PGWW-9VQ6

Vulnerability from github – Published: 2026-04-29 21:19 – Updated: 2026-05-08 01:31

Summary

n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration

Details

Impact

The MCP OAuth client registration endpoint accepted unauthenticated requests and stored client data without adequate resource controls. An unauthenticated remote attacker could exhaust server memory resources by sending large registration payloads, rendering the n8n instance unavailable. The MCP enable/disable toggle gates MCP access but did not restrict client registrations, meaning the endpoint is reachable regardless of whether MCP access is enabled on the instance.

The patches address the unbound registration with an upper bound of registered clients and disabling creation when MCP is disabled on the instance. Mean to restrict the payload size of requests already exist and can be used to control additional risks.

Patches

The issue has been fixed in n8n versions 1.123.32, 2.17.4, and 2.18.1. Users should upgrade to one of these versions or later to remediate the vulnerability.

Workarounds

If upgrading is not immediately possible, administrators should consider the following temporary mitigations: - Restrict network access to the n8n instance to prevent requests from untrusted sources. - Reduce the maximum accepted payload size by lowering the N8N_PAYLOAD_SIZE_MAX environment variable from its default value.

These workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.

Severity ?

7.5 (High)


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

8.7 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "n8n"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
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              "fixed": "1.123.32"
            }
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          "type": "ECOSYSTEM"
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    },
    {
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        "ecosystem": "npm",
        "name": "n8n"
      },
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  ],
  "aliases": [
    "CVE-2026-42236"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-29T21:19:07Z",
    "nvd_published_at": "2026-05-04T19:16:06Z",
    "severity": "HIGH"
  },
  "details": "## Impact\nThe MCP OAuth client registration endpoint accepted unauthenticated requests and stored client data without adequate resource controls. An unauthenticated remote attacker could exhaust server memory resources by sending large registration payloads, rendering the n8n instance unavailable. The MCP enable/disable toggle gates MCP access but did not restrict client registrations, meaning the endpoint is reachable regardless of whether MCP access is enabled on the instance.\n\nThe patches address the unbound registration with an upper bound of registered clients and disabling creation when MCP is disabled on the instance. Mean to restrict the payload size of requests already exist and can be used to control additional risks.\n\n## Patches\nThe issue has been fixed in n8n versions 1.123.32, 2.17.4, and 2.18.1. Users should upgrade to one of these versions or later to remediate the vulnerability.\n\n## Workarounds\nIf upgrading is not immediately possible, administrators should consider the following temporary mitigations:\n- Restrict network access to the n8n instance to prevent requests from untrusted sources.\n- Reduce the maximum accepted payload size by lowering the `N8N_PAYLOAD_SIZE_MAX` environment variable from its default value.\n\nThese workarounds do not fully remediate the risk and should only be used as short-term mitigation measures.",
  "id": "GHSA-49m9-pgww-9vq6",
  "modified": "2026-05-08T01:31:14Z",
  "published": "2026-04-29T21:19:07Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/n8n-io/n8n/security/advisories/GHSA-49m9-pgww-9vq6"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42236"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/n8n-io/n8n"
    }
  ],
  "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"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration"
}

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.

Action not permitted

CVE-2026-42236 (GCVE-0-2026-42236)

FKIE_CVE-2026-42236

GHSA-49M9-PGWW-9VQ6

Impact

Patches

Workarounds

Tags

Sightings

Nomenclature