CVE-2021-1738
📋 TL;DR
CVE-2021-1738 is an out-of-bounds write vulnerability in macOS image processing that could allow arbitrary code execution when processing a malicious image. This affects macOS users running vulnerable versions of Big Sur, Catalina, and Mojave. An attacker could exploit this to run malicious code with the privileges of the user opening the image.
💻 Affected Systems
- macOS
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Full system compromise via arbitrary code execution with user privileges, potentially leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Malware installation or data exfiltration when a user opens a malicious image file, potentially through phishing or compromised websites.
If Mitigated
Limited impact if systems are patched, users have limited privileges, and security controls prevent execution of untrusted files.
🎯 Exploit Status
Exploitation requires user interaction to open malicious image file. No public exploit code was available at disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave
Vendor Advisory: https://support.apple.com/en-us/HT212147
Restart Required: Yes
Instructions:
1. Open System Preferences > Software Update. 2. Install available updates. 3. Restart when prompted.
🔧 Temporary Workarounds
Disable automatic image preview
allPrevent automatic processing of image files in vulnerable applications
Use application sandboxing
allRun image processing applications in sandboxed environments
🧯 If You Can't Patch
- Restrict user privileges to limit impact of potential code execution
- Implement application allowlisting to prevent execution of unauthorized programs
🔍 How to Verify
Check if Vulnerable:
Check macOS version in System Preferences > About This Mac. If version is earlier than Big Sur 11.2, Catalina Security Update 2021-001, or Mojave Security Update 2021-001, system is vulnerable.Check Version:
sw_versVerify Fix Applied:
Verify macOS version shows Big Sur 11.2 or later, or that Security Update 2021-001 is installed for Catalina/Mojave.📡 Detection & Monitoring
Log Indicators:
- Unexpected process crashes in image processing components
- Unusual file access patterns for image files
Network Indicators:
- Downloads of suspicious image files from untrusted sources
SIEM Query:
Process creation events from image viewing/editing applications followed by suspicious child processes