n8n before 2.41.4 and 2.42.x before 2.42.1 contains an uncontrolled resource consumption vulnerability in the unauthenticated OAuth authorize endpoint, which resolves clients by URL path but stores the caller's raw identifier as the record key. Unauthenticated attackers can send identifiers differing only in their query string to create unlimited first-party client records that bypass the registration cap, growing the database until the disk fills.