CVE-2021-1776
📋 TL;DR
CVE-2021-1776 is an out-of-bounds write vulnerability in Apple's font processing that allows arbitrary code execution when processing malicious font files. This affects macOS, iOS, iPadOS, watchOS, and tvOS users running vulnerable versions. Attackers can exploit this to gain control of affected devices.
💻 Affected Systems
- macOS
- iOS
- iPadOS
- watchOS
- tvOS
📦 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 kernel-level privileges leading to complete data theft, persistence installation, and lateral movement within networks.
Likely Case
Remote code execution with user privileges when processing malicious font files from web content or documents.
If Mitigated
No impact if systems are patched or if font processing is restricted through security controls.
🎯 Exploit Status
Exploitation requires user interaction to process malicious font files. No public exploit code is known, but the vulnerability is serious enough that exploitation is plausible.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, watchOS 7.3, tvOS 14.4, iOS 14.4, iPadOS 14.4
Vendor Advisory: https://support.apple.com/en-us/HT212146
Restart Required: Yes
Instructions:
1. Open System Preferences > Software Update. 2. Install available updates. 3. Restart device when prompted. For managed devices, use MDM tools to deploy updates.
🔧 Temporary Workarounds
Restrict font installation
allPrevent installation of new font files through system policies or application restrictions.
Web content filtering
allBlock web fonts from untrusted sources using web proxies or browser extensions.
🧯 If You Can't Patch
- Implement application whitelisting to prevent execution of unknown processes
- Deploy network segmentation to isolate vulnerable systems from critical assets
🔍 How to Verify
Check if Vulnerable:
Check system version against affected versions. 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 matches or exceeds patched versions listed in fix_official.patch_version.📡 Detection & Monitoring
Log Indicators:
- Unexpected font file processing
- Application crashes related to font rendering
- Unusual process execution following font loading
Network Indicators:
- Downloads of font files from suspicious sources
- Font loading in web content from untrusted domains
SIEM Query:
Process creation events following font file access OR Application crash logs containing font-related components🔗 References
- https://support.apple.com/en-us/HT212146
- https://support.apple.com/en-us/HT212147
- https://support.apple.com/en-us/HT212148
- https://support.apple.com/en-us/HT212149
- https://support.apple.com/en-us/HT212146
- https://support.apple.com/en-us/HT212147
- https://support.apple.com/en-us/HT212148
- https://support.apple.com/en-us/HT212149
