Executive brief
n8n is a popular workflow automation platform that enables users to connect and automate business processes. An unauthenticated attacker can repeatedly register OAuth clients with arbitrarily large values in certain fields, causing the database to grow without limit and potentially degrading system availability. This attack requires no credentials or authentication, allowing any remote attacker to exhaust storage resources.
Technical details
The OAuth Dynamic Client Registration endpoint in n8n validates only the `redirect_uris` field for size limits, leaving `client_name` and `grant_types` fields bounded only by presence checks. An unauthenticated remote attacker can submit arbitrarily large values in these fields via the registration endpoint; these values are persisted to the database without sanitization. By repeatedly calling the registration endpoint with oversized payloads, an attacker can cause uncontrolled database growth, leading to denial of service or availability degradation. The attack requires only network access to the endpoint (no authentication, privileges, or user interaction). Patches in n8n 2.37.7 and 2.38.2 cap `client_name` to column length and restrict `grant_types` to valid server grant types.
Affected products
- n8n n8n < 2.37.7, >= 2.38.0 < 2.38.2
Timeline
- 2026-09-02: disclosed: Advisory published to GitHub Advisory Database
- 2026: patched: Fixed in n8n versions 2.37.7 and 2.38.2