CVE-2021-30843
📋 TL;DR
CVE-2021-30843 is a memory corruption vulnerability in Apple's dfont file processing that allows arbitrary code execution when a malicious dfont file is opened. This affects multiple Apple operating systems including iOS, iPadOS, macOS, tvOS, and watchOS. Attackers can exploit this to run malicious code with the privileges of the user opening the file.
💻 Affected Systems
- iOS
- iPadOS
- macOS
- tvOS
- watchOS
📦 What is this software?
Ipados by Apple
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 →Tvos by Apple
Watchos by Apple
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control of the device, potentially leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Malicious code execution in the context of the user opening the file, allowing data access, privilege escalation, or further network penetration.
If Mitigated
Limited impact with proper patch management and user awareness preventing malicious file execution.
🎯 Exploit Status
Exploitation requires user interaction to open a malicious dfont file. Public proof-of-concept code exists in the Full Disclosure mailing list references.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: iOS 14.8, iPadOS 14.8, macOS Big Sur 11.6, Security Update 2021-005 Catalina, tvOS 15, iOS 15, iPadOS 15, watchOS 8
Vendor Advisory: https://support.apple.com/en-us/HT212804
Restart Required: Yes
Instructions:
1. Open Settings/System Preferences. 2. Navigate to Software Update. 3. Install the latest available update. 4. Restart the device when prompted.
🔧 Temporary Workarounds
Block dfont file extensions
allPrevent opening of .dfont files through email filtering or endpoint protection
User awareness training
allEducate users not to open suspicious font files from untrusted sources
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized applications from running
- Deploy endpoint detection and response (EDR) solutions to monitor for suspicious font file processing
🔍 How to Verify
Check if Vulnerable:
Check system version against affected versions list. On macOS: System Preferences > About This Mac. On iOS/iPadOS: Settings > General > About.Check Version:
macOS: sw_vers -productVersion; iOS/iPadOS: Settings > General > About > VersionVerify Fix Applied:
Verify system version is at or above the patched versions listed in the fix information.📡 Detection & Monitoring
Log Indicators:
- Unusual font file processing events
- Application crashes related to font loading
- Process creation from font-related applications
Network Indicators:
- Downloads of font files from suspicious sources
- Outbound connections after font file processing
SIEM Query:
process_name:font* AND (event_type:process_creation OR event_type:file_access) AND file_extension:dfont🔗 References
- http://seclists.org/fulldisclosure/2021/Oct/61
- http://seclists.org/fulldisclosure/2021/Oct/62
- http://seclists.org/fulldisclosure/2021/Oct/63
- https://support.apple.com/en-us/HT212804
- https://support.apple.com/en-us/HT212805
- https://support.apple.com/en-us/HT212807
- https://support.apple.com/en-us/HT212814
- https://support.apple.com/en-us/HT212815
- https://support.apple.com/en-us/HT212819
- http://seclists.org/fulldisclosure/2021/Oct/61
- http://seclists.org/fulldisclosure/2021/Oct/62
- http://seclists.org/fulldisclosure/2021/Oct/63
- https://support.apple.com/en-us/HT212804
- https://support.apple.com/en-us/HT212805
- https://support.apple.com/en-us/HT212807
- https://support.apple.com/en-us/HT212814
- https://support.apple.com/en-us/HT212815
- https://support.apple.com/en-us/HT212819
