CVE-2011-3216 in Mac OS X
Summary
by MITRE
The kernel in Apple Mac OS X before 10.7.2 does not properly implement the sticky bit for directories, which might allow local users to bypass intended permissions and delete files via an unlink system call.
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Analysis
by VulDB Data Team • 01/19/2025
The vulnerability described in CVE-2011-3216 represents a critical flaw in the Unix-style permission model implementation within Apple Mac OS X kernel versions prior to 10.7.2. This issue stems from the improper handling of the sticky bit attribute on directories, a fundamental security mechanism that has been part of Unix-like operating systems since the early days of computing. The sticky bit, when set on a directory, typically restricts file deletion rights to only the file owner, directory owner, or privileged users. This protection mechanism is essential for maintaining the integrity of shared directories and preventing unauthorized file removal operations.
The technical implementation flaw manifests when the kernel fails to properly validate whether a user attempting to delete a file via unlink system call possesses the necessary permissions. In systems with properly implemented sticky bit functionality, users should only be able to delete files they own or have explicit write permissions for within a directory. However, the vulnerability allows local attackers to bypass these protections by exploiting the kernel's insufficient validation of the sticky bit enforcement, enabling them to perform unlink operations on files they would normally not be permitted to delete. This represents a direct violation of the principle of least privilege and undermines the fundamental security model of the operating system.
The operational impact of this vulnerability extends beyond simple permission bypass, as it provides attackers with the ability to manipulate file systems in ways that could compromise system integrity and data security. Local users with minimal privileges could potentially remove critical system files, log files, or user data, leading to system instability or data loss. The vulnerability affects the core kernel functionality, making it particularly dangerous as it operates at the lowest level of the operating system where security controls are most critical. This flaw could be exploited in various attack scenarios including privilege escalation attempts, data destruction campaigns, or system compromise operations where an attacker seeks to remove forensic evidence or critical system components.
The vulnerability maps directly to CWE-276, which describes improper file permissions, and aligns with ATT&CK technique T1068, which covers privilege escalation through local exploitation. Organizations running affected Mac OS X versions face significant risk exposure, as the vulnerability requires no network connectivity and can be exploited by any local user with access to the system. The fix implemented by Apple in Mac OS X 10.7.2 involved correcting the kernel's directory permission validation logic to properly enforce the sticky bit semantics, ensuring that unlink operations respect the directory ownership and permission settings as originally intended. System administrators should prioritize patching affected systems, as the vulnerability represents a fundamental flaw in the operating system's security architecture that could be leveraged for more sophisticated attacks.
This vulnerability demonstrates the critical importance of proper kernel implementation of security features and highlights how seemingly minor flaws in core system components can have significant security implications. The issue also underscores the necessity of thorough testing and validation of permission models, particularly in multi-user environments where proper access controls are essential for maintaining system security and data integrity.