UIPI

User Interface Privilege Isolation (UIPI) is a security feature implemented by Microsoft Windows that restricts how processes at different privilege levels can interact with each other's user interfaces. It is part of the broader Windows integrity mechanism used to enforce separation between processes with different rights, such as those controlled by User Account Control (UAC).

Under UIPI, certain inter-process UI actions are blocked when the caller has a lower integrity level than the target window. For example, sending input, posting messages, or attaching input threads to a window owned by a higher-privilege process may be denied, preventing lower-privilege processes from manipulating or spying on high-privilege UI.

By isolating UI, UIPI helps mitigate privilege escalation and credential theft that rely on manipulating the UI, such as user impersonation prompts or deceptive dialog boxes. However, legitimate cross-process UI workflows may require design adjustments, such as running components at the same integrity level or using explicit secure prompts and shared UI components.

UIPI is one aspect of Windows security posture and has influenced software design, particularly for applications with elevated privileges and for browsers and helper processes that interact with the system UI. It continues to be maintained in modern Windows releases as part of ongoing protection against UI-based attacks.

Related concepts include User Account Control and Windows integrity levels.