CVE-2019-8533 in macOS
Summary
by MITRE
A lock handling issue was addressed with improved lock handling. This issue is fixed in macOS Mojave 10.14.4. A Mac may not lock when disconnecting from an external monitor.
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Analysis
by VulDB Data Team • 05/21/2020
The vulnerability identified as CVE-2019-8533 represents a critical lock handling flaw in macOS operating systems that affects the automatic screen locking mechanism when external displays are disconnected. This issue stems from improper synchronization between the system's power management subsystem and display handling components, creating a scenario where the security posture of macOS devices becomes compromised during external monitor disconnection events. The vulnerability specifically impacts systems running macOS Mojave versions prior to 10.14.4, where the lock screen functionality fails to activate correctly when users disconnect external displays such as projectors, monitors, or docking stations.
The technical root cause of this vulnerability lies in the insufficient handling of display connection state changes within the operating system's security framework. When an external monitor is disconnected, the system should automatically trigger the screen lock mechanism to prevent unauthorized access to the device's contents. However, due to flawed state management in the display subsystem, the lock command fails to execute properly, leaving the device vulnerable to potential unauthorized access. This issue is classified under CWE-284 which addresses improper access control mechanisms and specifically relates to inadequate lock handling procedures within the operating system's security architecture. The flaw manifests when the system fails to recognize that the display state has changed from connected to disconnected, thereby preventing the automatic activation of the screen lock feature that should occur in response to such disconnection events.
The operational impact of CVE-2019-8533 extends beyond simple inconvenience to represent a significant security risk for macOS users in enterprise and sensitive environments. When a Mac device remains unlocked after disconnecting from an external monitor, unauthorized individuals who gain physical access to the device can potentially access confidential data, applications, and system resources without proper authentication. This vulnerability particularly affects users who frequently connect their devices to external displays in shared office environments, conference rooms, or public spaces where physical security cannot be guaranteed. The risk is exacerbated by the fact that the issue occurs automatically during routine operations, making it difficult for users to maintain awareness of their device's security status. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1077 which involves the exploitation of legitimate user privileges and system access controls to gain unauthorized access to systems, as the compromised lock mechanism essentially provides unauthorized access to devices that should be secured.
Organizations and individual users affected by this vulnerability should implement immediate mitigation strategies while awaiting the official patch deployment. The primary recommendation involves updating to macOS Mojave version 10.14.4 or later, which contains the necessary fixes for the lock handling mechanism. System administrators should conduct comprehensive inventory checks to identify all affected devices and prioritize patch deployment across enterprise environments. Additionally, users can implement manual lock procedures by configuring automatic screen lock settings to activate after brief periods of inactivity, creating a secondary security layer. The vulnerability demonstrates the importance of proper lock handling in preventing unauthorized physical access to computing devices and highlights the need for robust testing of security features during system updates and configuration changes. Security teams should also consider implementing additional monitoring controls to detect unusual device access patterns that might indicate successful exploitation of this vulnerability, particularly in environments where physical security cannot be fully trusted.