CVE-2020-27931
📋 TL;DR
CVE-2020-27931 is a memory corruption vulnerability in Apple's font processing that allows arbitrary code execution when processing malicious font files. It affects iOS, iPadOS, macOS, watchOS, and tvOS users. Attackers can exploit this to take control of affected devices.
💻 Affected Systems
- iOS
- iPadOS
- macOS
- watchOS
- tvOS
📦 What is this software?
Ipados by Apple
Tvos by Apple
Watchos by Apple
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining root privileges and persistent access to the device.
Likely Case
Malicious font file delivered via phishing or compromised website leads to remote code execution with user privileges.
If Mitigated
Attack fails due to patched systems or blocked font file delivery mechanisms.
🎯 Exploit Status
Exploitation requires user to open malicious font file, but no authentication needed once file is processed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: iOS 14.0+, iPadOS 14.0+, macOS Big Sur 11.1+, Security Update 2020-001 Catalina+, Security Update 2020-007 Mojave+, macOS Big Sur 11.0.1+, watchOS 7.0+, tvOS 14.0+
Vendor Advisory: https://support.apple.com/en-us/HT211843
Restart Required: Yes
Instructions:
1. Go to Settings > General > Software Update on iOS/iPadOS/watchOS/tvOS. 2. Install available updates. 3. For macOS, go to Apple menu > System Preferences > Software Update. 4. Install all security updates. 5. Restart device after installation.
🔧 Temporary Workarounds
Block suspicious font files
allConfigure email/web filters to block font files from untrusted sources.
User education
allTrain users not to open font files from unknown sources.
🧯 If You Can't Patch
- Isolate affected devices from internet and restrict network access
- Implement application whitelisting to prevent unauthorized font processing
🔍 How to Verify
Check if Vulnerable:
Check system version against affected versions list. On macOS: 'sw_vers -productVersion'. On iOS/iPadOS: Settings > General > About > Version.Check Version:
macOS: 'sw_vers -productVersion', iOS/iPadOS: Check in Settings > General > AboutVerify Fix Applied:
Verify system version matches or exceeds patched versions listed in fix_official section.📡 Detection & Monitoring
Log Indicators:
- Unexpected font file processing
- Crash logs from fontd or font processing services
- Unusual process execution following font file access
Network Indicators:
- Downloads of font files from suspicious sources
- Font file transfers via email or web
SIEM Query:
process_name:fontd AND (event_type:process_execution OR event_type:crash)🔗 References
- https://support.apple.com/en-us/HT211843
- https://support.apple.com/en-us/HT211844
- https://support.apple.com/en-us/HT211850
- https://support.apple.com/en-us/HT211931
- https://support.apple.com/en-us/HT212011
- https://support.apple.com/en-us/HT211843
- https://support.apple.com/en-us/HT211844
- https://support.apple.com/en-us/HT211850
- https://support.apple.com/en-us/HT211931
- https://support.apple.com/en-us/HT212011
