CVE-2015-5849 in Mac OS X
Summary
by MITRE
The filtering implementation in AppleEvents in Apple OS X before 10.11 mishandles attempts to send events to a different user, which allows attackers to bypass intended access restrictions by leveraging a screen-sharing connection.
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Analysis
by VulDB Data Team • 11/21/2024
The vulnerability identified as CVE-2015-5849 represents a critical security flaw in Apple's operating system implementation of AppleEvents functionality within OS X versions prior to 10.11. This issue stems from inadequate input validation and access control mechanisms that govern how AppleEvents are processed and transmitted between different user contexts. The vulnerability specifically targets the AppleEvents subsystem which serves as a communication framework allowing applications to send messages and commands to each other across system boundaries. When attempting to send AppleEvents to processes running under different user accounts, the system fails to properly enforce access restrictions that should normally prevent cross-user communication.
The technical implementation flaw lies in how the system handles privilege escalation through AppleEvents when a screen-sharing connection is active. AppleEvents are designed to facilitate inter-process communication and system-level operations, but the filtering mechanism in affected versions does not adequately validate the identity and permissions of the sending process. This oversight creates a pathway where an attacker with access to a screen-sharing session can manipulate AppleEvents to execute commands or access resources that would normally be restricted to different user contexts. The vulnerability leverages the inherent trust relationships within the AppleEvents system to bypass security boundaries that should normally prevent unauthorized cross-user access.
Operationally, this vulnerability poses significant risks to system integrity and user privacy within environments where screen sharing is utilized. Attackers can exploit this weakness to gain unauthorized access to files, applications, or system resources belonging to other users on the same machine. The impact extends beyond simple information disclosure to potentially enable privilege escalation attacks where malicious actors can execute code with elevated privileges or access sensitive system functions. The screen-sharing context provides a legitimate entry point that makes exploitation more likely in enterprise environments where remote access and collaboration tools are commonly deployed. Security researchers have noted that this vulnerability can be particularly dangerous in multi-user environments such as shared workstations, public computing facilities, or corporate networks where multiple users share the same physical hardware.
Mitigation strategies for CVE-2015-5849 require immediate system updates to OS X 10.11 or later versions where Apple has addressed the filtering implementation issues. Organizations should also implement network segmentation and access controls to limit screen-sharing capabilities to trusted users and environments. System administrators should review and tighten AppleEvents permissions through the Security & Privacy preferences, disabling unnecessary AppleEvents access for applications that do not require such functionality. The vulnerability aligns with CWE-284, which describes improper access control mechanisms, and maps to ATT&CK technique T1059.007 for AppleScript and AppleEvents execution. Additional defensive measures include monitoring for unusual AppleEvents activity, implementing application whitelisting policies, and conducting regular security assessments of screen-sharing configurations to identify and remediate potential attack vectors.