CVE-2021-1834
📋 TL;DR
CVE-2021-1834 is an out-of-bounds write vulnerability in macOS that allows a malicious application to execute arbitrary code with kernel privileges. This affects macOS Big Sur, Catalina, and Mojave systems. Successful exploitation gives attackers complete control over the affected system.
💻 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
Complete system compromise with kernel-level privileges, allowing attackers to install persistent malware, steal sensitive data, or use the system as a foothold for lateral movement.
Likely Case
Malicious applications exploiting this vulnerability to gain full system control, potentially leading to data theft, ransomware deployment, or credential harvesting.
If Mitigated
Limited impact if systems are fully patched, applications are from trusted sources only, and proper endpoint protection is in place.
🎯 Exploit Status
Exploitation requires a malicious application to be executed on the target system. No public exploit code was available at disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version that fixes this: macOS Big Sur 11.3, Security Update 2021-002 for Catalina, Security Update 2021-003 for Mojave
Vendor Advisory: URL to vendor advisory if known: https://support.apple.com/en-us/HT212325
Restart Required: Yes
Instructions:
Step-by-step patching instructions: 1. Open System Preferences > Software Update. 2. Click 'Update Now' to install available security updates. 3. Restart the system when prompted.
🔧 Temporary Workarounds
Application Restriction
allWhat this does: Restrict application installation to App Store only to prevent malicious applications from being installed.
sudo spctl --master-enable
sudo spctl --enable --label "Mac App Store"
sudo spctl --enable --label "Developer ID"
🧯 If You Can't Patch
- Risk reduction step 1: Implement application allowlisting to prevent unauthorized applications from executing.
- Risk reduction step 2: Use endpoint detection and response (EDR) solutions to monitor for suspicious kernel-level activity.
🔍 How to Verify
Check if Vulnerable:
Commands or steps to check if vulnerable: Check macOS version with 'sw_vers' command. If version is: Big Sur < 11.3, Catalina without 2021-002 update, or Mojave without 2021-003 update, system is vulnerable.Check Version:
Command to check current version: sw_versVerify Fix Applied:
Commands or steps to verify the fix worked: Run 'sw_vers' and verify version is Big Sur 11.3 or higher, or check that Catalina/Mojave security updates are installed via System Preferences > Software Update.📡 Detection & Monitoring
Log Indicators:
- What to look for in logs: Unusual kernel extensions loading, unexpected privilege escalation attempts, or suspicious application execution with elevated privileges.
Network Indicators:
- Network-based detection: Outbound connections from kernel processes or system-level services to suspicious external IPs.
SIEM Query:
Example SIEM/detection query if applicable: (process_name:kernel AND parent_process:malicious_app) OR (privilege_escalation:true AND os:macos)