CVE-2026-42236: N8n Denial of Service Vulnerability
HIGHCVE-2026-42236 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting N8n libraries in the npm ecosystem. The issue involves n8n vulnerable to unauthenticated denial of service via mcp client registration. Remediation is available by upgrading affected packages to version 1.123.32, 2.18.1, 2.17.4.
CVE-2026-42236 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
How to Fix CVE-2026-42236
To remediate this vulnerability, upgrade all affected N8n dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install n8n@1.123.32npm install n8n@2.18.1npm install n8n@2.17.4Run the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls n8nHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-42236, inspect your project dependencies using npm:
npm ls n8nAnalyze the terminal output to locate any version of N8n in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.123.32), your application is affected.
Note: The npm ls n8n command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In N8n, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-42236 Affected N8n Versions
3 component(s)References
Frequently Asked Questions
What is CVE-2026-42236?
Which N8n versions are affected?
What version fixes CVE-2026-42236?
Is n8n affected?
What is the CVSS score of CVE-2026-42236?
What CWE is associated with CVE-2026-42236?
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Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-49m9-pgww-9vq6",
"modified" : "2026-05-08T01:31:14Z",
"published" : "2026-04-29T21:19:07Z",
"aliases" : [ "CVE-2026-42236" ],
"summary" : "n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration",
"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.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
}, {
"type" : "CVSS_V4",
"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"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "n8n"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "1.123.32"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "n8n"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.18.0"
}, {
"fixed" : "2.18.1"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "n8n"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.0.0"
}, {
"fixed" : "2.17.4"
} ]
} ]
} ],
"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"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-770" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-04-29T21:19:07Z",
"nvd_published_at" : "2026-05-04T19:16:06Z"
}
}