CVE-2021-1840
📋 TL;DR
CVE-2021-1840 is a memory corruption vulnerability in macOS that allows local attackers to elevate their privileges. This affects macOS Big Sur, Catalina, and Mojave systems. An attacker with local access could gain higher privileges than intended.
💻 Affected Systems
- macOS
📦 What is this software?
Macos by Apple
macOS is Apple's desktop and laptop operating system powering Mac computers used by millions of professionals, developers, creative professionals, and enterprise users worldwide. Built on a Unix foundation with the Darwin kernel and modern Cocoa frameworks, macOS delivers a seamless ecosystem integr...
Learn more about Macos →⚠️ Risk & Real-World Impact
Worst Case
Local attacker gains root privileges, potentially taking full control of the system, accessing sensitive data, and installing persistent malware.
Likely Case
Local user or malware with initial access escalates to administrator privileges, enabling further system compromise and lateral movement.
If Mitigated
With proper patching and least privilege principles, impact is limited to isolated systems with no privilege escalation paths.
🎯 Exploit Status
Requires local access and some technical knowledge to exploit memory corruption issues. No public exploit code identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: macOS Big Sur 11.3, Security Update 2021-002 Catalina, Security Update 2021-003 Mojave
Vendor Advisory: https://support.apple.com/en-us/HT212325
Restart Required: Yes
Instructions:
1. Open System Preferences > Software Update. 2. Install available updates. 3. Restart when prompted. 4. Verify update completed successfully.
🔧 Temporary Workarounds
Restrict local access
allLimit physical and remote local access to affected systems
🧯 If You Can't Patch
- Implement strict least privilege principles - ensure users only have necessary permissions
- Monitor for privilege escalation attempts and unusual administrative activity
🔍 How to Verify
Check if Vulnerable:
Check macOS version: System Preferences > About This Mac. If version is Big Sur < 11.3, Catalina without 2021-002 update, or Mojave without 2021-003 update, system is vulnerable.Check Version:
sw_versVerify Fix Applied:
Verify macOS version shows Big Sur 11.3 or later, or Catalina/Mojave with appropriate security updates installed.📡 Detection & Monitoring
Log Indicators:
- Unexpected privilege escalation events in system logs
- Processes running with unexpected elevated privileges
Network Indicators:
- None - local exploit only
SIEM Query:
Search for process creation events where parent process unexpectedly spawns child with higher privileges