CVE-2021-30892: Apple macOS Privilege Escalation Flaw

CVE-2021-30892 Overview

CVE-2021-30892 is an inherited permissions issue affecting Apple macOS operating systems that allows malicious applications to modify protected parts of the file system. This vulnerability stems from improper permission inheritance, enabling attackers to bypass file system protections and alter critical system components through a locally executed malicious application.

Critical Impact

A malicious application may be able to modify protected parts of the file system, potentially compromising system integrity and security controls.

Affected Products

• Apple macOS Monterey (versions prior to 12.0.1)
• Apple macOS Big Sur (versions prior to 11.6.1)
• Apple Mac OS X 10.15.7 (Catalina - prior to Security Update 2021-007)

Discovery Timeline

• 2021-08-24 - CVE-2021-30892 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-30892

Vulnerability Analysis

This vulnerability is classified under CWE-732 (Incorrect Permission Assignment for Critical Resource). The flaw exists in how macOS handles inherited permissions for certain file system operations. When permissions are improperly inherited, a malicious application running with standard user privileges can exploit this weakness to write to or modify files in protected areas of the file system that should be restricted.

The attack requires local access and user interaction, typically through convincing a user to execute a malicious application. Once executed, the application can leverage the inherited permissions flaw to bypass System Integrity Protection (SIP) mechanisms and other file system safeguards that normally protect critical macOS components.

Root Cause

The root cause lies in improper handling of permission inheritance within the macOS file system security model. Specifically, certain operations failed to properly restrict permissions when files or directories inherited access rights from parent objects, allowing escalated write access to protected system areas.

Attack Vector

The attack requires a malicious application to be executed locally on the target system. The attacker must convince the user to run the application, after which the vulnerability can be exploited without additional user interaction. The exploitation path targets the file system permission inheritance mechanism:

1. Attacker crafts a malicious application designed to exploit the permission inheritance flaw
2. User downloads and executes the malicious application
3. The application identifies protected file system locations with improper permission inheritance
4. The application leverages the inherited permissions to write to or modify protected files
5. System integrity is compromised, potentially allowing persistence, privilege escalation, or security control bypass

Detection Methods for CVE-2021-30892

Indicators of Compromise

• Unexpected modifications to files in /System, /Library, or other SIP-protected directories
• Applications with unusual write access to protected file system locations
• Suspicious process activity attempting to modify system configuration files
• File integrity monitoring alerts for protected macOS system files

Detection Strategies

• Implement file integrity monitoring (FIM) for critical macOS system directories
• Monitor for applications attempting write operations to SIP-protected paths
• Review system logs for permission-related errors or unexpected file modifications
• Deploy endpoint detection tools capable of identifying permission abuse patterns on macOS

Monitoring Recommendations

• Enable and monitor macOS Unified Logging for file system access events
• Configure alerts for modifications to critical system files and directories
• Utilize SentinelOne Singularity Platform for real-time behavioral analysis and threat detection on macOS endpoints
• Regularly audit installed applications and their associated permissions

How to Mitigate CVE-2021-30892

Immediate Actions Required

• Update to macOS Monterey 12.0.1 or later immediately
• Apply Security Update 2021-007 for macOS Catalina 10.15.7
• Update to macOS Big Sur 11.6.1 or later
• Restrict installation of applications to trusted sources only (App Store and identified developers)
• Review recently installed applications for suspicious behavior

Patch Information

Apple has addressed this vulnerability with additional permission restrictions in the following releases:

• macOS Monterey 12.0.1 - Includes fix for CVE-2021-30892
• macOS Big Sur 11.6.1 - Includes fix for CVE-2021-30892
• Security Update 2021-007 Catalina - Includes fix for CVE-2021-30892

Organizations should prioritize updating all affected macOS systems to the patched versions listed above.

Workarounds

• Enable Gatekeeper to restrict application execution to verified developers
• Implement application allowlisting to prevent execution of untrusted applications
• Ensure System Integrity Protection (SIP) remains enabled on all macOS systems
• Limit local administrator privileges and enforce principle of least privilege
• Deploy endpoint protection solutions for additional runtime protection against malicious applications