CVE-2026-42236
Memory Exhaustion via Unauthenticated MCP Client Registration in n8n
Publication date: 2026-05-04
Last updated on: 2026-05-06
Assigner: GitHub, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| n8n | n8n | to 1.123.32 (exc) |
| n8n | n8n | From 2.17.0 (inc) to 2.17.4 (inc) |
| n8n | n8n | 2.18.0 |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-770 | 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. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
This vulnerability exists in the n8n 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 proper resource controls. Because of this, an unauthenticated remote attacker could send large registration payloads to the endpoint, exhausting the server's memory resources and causing the n8n instance to become unavailable.
Additionally, the MCP enable/disable toggle, which controls MCP access, did not restrict client registrations, meaning the vulnerable endpoint was reachable regardless of whether MCP access was enabled or disabled on the instance.
This issue has been fixed in versions 1.123.32, 2.17.4, and 2.18.1.
How can this vulnerability impact me? :
The vulnerability allows an unauthenticated remote attacker to exhaust the server's memory resources by sending large registration payloads to the MCP OAuth client registration endpoint.
This can render the n8n instance unavailable, causing a denial of service (DoS) condition that disrupts workflow automation and any dependent business processes.
What immediate steps should I take to mitigate this vulnerability?
To mitigate this vulnerability, you should upgrade your n8n instance to one of the patched versions: 1.123.32, 2.17.4, or 2.18.1.
Since the MCP OAuth client registration endpoint accepts unauthenticated requests and can be abused to exhaust server memory, applying the patch will ensure that client data is stored with adequate resource controls and prevent unauthenticated attackers from causing denial of service.