GHSA-49m9-pgww-9vq6: n8n Vulnerable to Unauthenticated Denial of Service via MCP Client Registration

Summary

The MCP OAuth client registration endpoint in n8n accepted unauthenticated requests and stored client data without adequate resource controls. A remote attacker can exhaust server memory with large registration payloads, making the instance unavailable, and the endpoint remains reachable even when MCP is disabled.

Mitigation

Fixed in n8n 1.123.32, 2.17.4, and 2.18.1; upgrade to one of these versions or later. If upgrading is not immediately possible, restrict network access to the n8n instance to untrusted sources and lower the N8N_PAYLOAD_SIZE_MAX environment variable from its default value. These workarounds do not fully remediate the risk and are short-term measures only.

Affected packages in the Exposure Registry

Matched by package name and ecosystem. Each entry shows whether the package delegates to a language model and how many tracked packages depend on it.

• n8nnpmLLM dependency since 2026-02-10

Topics

• Model Context Protocol

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• LowCloakFEM: Agentic FEM Code Generation for Red-Teaming Computational Resource ExhaustionSimilar attack · Arxiv (cs.CR + cs.CL + cs.LG)
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