CVE-2021-30841
📋 TL;DR
This vulnerability allows arbitrary code execution by processing a maliciously crafted dfont file. It affects Apple devices running vulnerable versions of iOS, iPadOS, macOS, tvOS, and watchOS. Attackers could exploit this to gain control of affected systems.
💻 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
Full system compromise with attacker gaining root privileges and persistent access to the device.
Likely Case
Malicious application or file could execute arbitrary code with user privileges, potentially leading to data theft or further system compromise.
If Mitigated
With proper patching, no impact. Without patching but with application sandboxing and other security controls, impact may be limited to the application context.
🎯 Exploit Status
Exploitation requires user interaction to process a malicious dfont file. Public disclosures include technical details that could facilitate exploitation.
🛠️ 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. Go to Settings > General > Software Update on iOS/iPadOS/watchOS. 2. For macOS, go to System Preferences > Software Update. 3. Download and install the latest available update. 4. Restart the device after installation.
🔧 Temporary Workarounds
Restrict dfont file processing
allBlock or restrict processing of dfont files through application controls or file type restrictions.
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized applications from processing dfont files.
- Educate users to avoid opening untrusted dfont files from unknown sources.
🔍 How to Verify
Check if Vulnerable:
Check current OS version against affected versions list. On iOS/iPadOS: Settings > General > About > Version. On macOS: Apple menu > About This Mac > Overview.Check Version:
On macOS: sw_vers -productVersion. On iOS/iPadOS: UIDevice.current.systemVersion (programmatic).Verify Fix Applied:
Verify OS version is at or above the patched versions listed in the fix information.📡 Detection & Monitoring
Log Indicators:
- Unusual process creation from font-related services
- Crash reports from font processing components
Network Indicators:
- Downloads of dfont files from untrusted sources
SIEM Query:
Process creation where parent process is fontd or similar font service and command line contains dfont file path🔗 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
