n8n: Unauthenticated Persistent Storage Exhaustion via OAuth Dynamic Client Registration Endpoint

Impact

The OAuth Dynamic Client Registration endpoints validated field sizes only for redirect_uris, leaving client_name and grant_types bounded by presence checks alone. An unauthenticated remote caller could submit arbitrarily large values in either field and have them persisted to the database. Repeated registration therefore grew persistent storage without limit and without any account on the instance. The patch caps client_name at its column length and limits grant_types to the grant types the server actually implements, with the array capped at that count.

Patches

The issue has been fixed in n8n versions 2.37.7 and 2.38.2. 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 so that only trusted clients can reach it.
• Place the instance behind a reverse proxy configured to enforce strict request body size limits below the default 16 MiB.
• Monitor database size for unexpected growth and audit the oauth_clients table for anomalous entries.

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