Insecure Direct Object References (IDOR) occur when an application provides direct access to objects based on user-supplied input. In the provided URLs, the userid parameter is directly referenced, which can allow attackers to manipulate these references to access unauthorized data. This vulnerability can lead to unauthorized access to other users' profiles by simply changing the userid parameter value. The other vulnerabilities listed (Improper error handling, Race condition, Weak or default configurations) do not directly relate to the issue demonstrated by the URLs.