CVE-2019-8858 in macOS
Summary
by MITRE • 10/28/2020
A logic issue was addressed with improved state management. This issue is fixed in macOS Catalina 10.15.1, Security Update 2019-001, and Security Update 2019-006. A user who shares their screen may not be able to end screen sharing.
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Analysis
by VulDB Data Team • 11/29/2020
This vulnerability represents a logic flaw in macOS Catalina's screen sharing implementation that affects user session management during collaborative work scenarios. The issue stems from inadequate state handling within the screen sharing subsystem, specifically when users attempt to terminate shared sessions. According to the security advisory, the problem manifests when a user initiates screen sharing and subsequently attempts to end the sharing session, creating a potential denial of service condition where the sharing cannot be properly terminated.
The technical root cause involves improper state management within the operating system's screen sharing framework, which fails to properly transition between active and inactive states during the termination process. This logic flaw creates a condition where the system becomes unresponsive to user commands intended to end screen sharing sessions, effectively locking users into shared sessions. The vulnerability falls under the category of improper state management as defined by CWE-691, which addresses insufficient control of the state of an object or process. The issue represents a failure in the system's ability to properly handle session lifecycle events, particularly the transition from active sharing to termination state.
The operational impact of this vulnerability extends beyond simple user inconvenience to potentially compromise security and productivity in enterprise environments. When screen sharing cannot be properly terminated, it creates persistent access points that may allow unauthorized parties to maintain visibility into shared workspaces. This situation particularly affects collaborative work scenarios where multiple users may be involved in shared sessions, and the inability to properly end sessions can lead to extended exposure of sensitive information. The vulnerability also impacts user experience by creating situations where users cannot effectively control their sharing sessions, potentially leading to forced logout scenarios or requiring system restarts to regain normal functionality.
Security updates for this vulnerability were released as part of macOS Catalina 10.15.1, Security Update 2019-001, and Security Update 2019-006, which address the underlying state management issues in the screen sharing subsystem. Organizations should ensure all macOS systems are updated to these versions to mitigate the risk of persistent screen sharing sessions that cannot be properly terminated. The fix implements improved state transition handling that properly manages the lifecycle of screen sharing sessions, ensuring that when users attempt to end sharing, the system properly transitions from active to inactive states and releases all associated resources. This remediation aligns with the ATT&CK framework's approach to privilege escalation and persistence by addressing a condition that could potentially be exploited to maintain unauthorized access to shared workspaces. System administrators should prioritize deployment of these security updates, particularly in environments where screen sharing is frequently used for collaborative work, remote support, or training scenarios where proper session management is critical for maintaining security posture and user productivity.