Missing authorization is a common security flaw where an application assumes a user's identity (authentication) is enough to grant access, skipping the crucial step of checking their specific privileges. Think of it like having a key to enter a building (authentication) but then being able to walk into any office or safe without further checks. This allows attackers, including other authenticated users, to access data or perform functions they shouldn't, such as viewing another user's private information, modifying account settings, or deleting critical resources. To prevent this, developers must implement a consistent and robust authorization layer that validates permissions for every request involving sensitive resources or actions. This involves defining clear roles and permissions, checking them against the requested operation and the target data (e.g., ensuring User A can only edit their own profile, not User B's), and centralizing these checks to avoid inconsistencies. Relying solely on UI element hiding is insufficient, as direct API calls or modified requests can easily bypass such superficial controls.