CVE-2021-30969
📋 TL;DR
This macOS vulnerability allows malicious URLs to trigger unexpected JavaScript execution from local files. Attackers could potentially execute arbitrary code by tricking users into opening specially crafted URLs. Affects macOS Catalina and Big Sur users who haven't applied security updates.
💻 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
Remote code execution leading to full system compromise, data theft, or malware installation
Likely Case
Limited JavaScript execution in browser context, potentially stealing session cookies or performing actions on behalf of user
If Mitigated
No impact if patched or if user avoids clicking suspicious URLs
🎯 Exploit Status
Requires social engineering to deliver malicious URL; Apple has not disclosed technical details
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security Update 2021-008 for Catalina, macOS Big Sur 11.6.2
Vendor Advisory: https://support.apple.com/en-us/HT212979
Restart Required: Yes
Instructions:
1. Open System Preferences > Software Update
2. Install Security Update 2021-008 (Catalina) or macOS Big Sur 11.6.2
3. Restart computer when prompted
🔧 Temporary Workarounds
URL validation browser extension
allInstall browser extensions that validate URLs before loading
Disable automatic URL handling
allConfigure browser to prompt before opening URLs from external applications
🧯 If You Can't Patch
- Educate users to avoid clicking suspicious URLs, especially from untrusted sources
- Implement web filtering to block known malicious domains and URL patterns
🔍 How to Verify
Check if Vulnerable:
Check macOS version: Catalina users without Security Update 2021-008 or Big Sur users below 11.6.2 are vulnerableCheck Version:
sw_versVerify Fix Applied:
Verify macOS version shows Catalina with Security Update 2021-008 or Big Sur 11.6.2 or higher📡 Detection & Monitoring
Log Indicators:
- Browser logs showing unexpected file:// URL access
- Console logs with JavaScript execution errors from local files
Network Indicators:
- Unusual outbound connections following URL clicks
- DNS requests for suspicious domains
SIEM Query:
source="browser.logs" AND (url="file://*" OR javascript_execution="local_file")