CVE-2021-40531
📋 TL;DR
CVE-2021-40531 is a vulnerability in Sketch design software that allows attackers to bypass macOS file quarantine protections through malicious library feeds. This enables remote code execution by automatically downloading and executing files without user interaction. Users of Sketch versions before 75 on macOS are affected.
💻 Affected Systems
- Sketch
📦 What is this software?
Sketch by Sketch
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through remote code execution, allowing attackers to install malware, steal data, or gain persistent access to the system.
Likely Case
Malware installation through malicious Sketch libraries, potentially leading to data theft, ransomware deployment, or credential harvesting.
If Mitigated
Limited impact if proper network segmentation and endpoint protection are in place, though local system compromise is still possible.
🎯 Exploit Status
Exploitation requires user to interact with malicious library feed. Proof of concept demonstrates terminal command execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 75 and later
Vendor Advisory: https://www.sketch.com/updates/#version-75
Restart Required: Yes
Instructions:
1. Open Sketch application. 2. Go to Sketch menu > Check for Updates. 3. Install version 75 or later. 4. Restart Sketch after installation.
🔧 Temporary Workarounds
Disable automatic library downloads
allPrevent Sketch from automatically downloading library content
Manual configuration in Sketch preferences under Libraries tab
Use macOS Gatekeeper restrictions
linuxConfigure macOS to only allow apps from App Store and identified developers
sudo spctl --master-enable
System Preferences > Security & Privacy > General
🧯 If You Can't Patch
- Disable Sketch library feeds feature entirely
- Implement application whitelisting to prevent unauthorized execution
🔍 How to Verify
Check if Vulnerable:
Check Sketch version in application menu: Sketch > About Sketch. If version is below 75, system is vulnerable.Check Version:
defaults read /Applications/Sketch.app/Contents/Info.plist CFBundleShortVersionStringVerify Fix Applied:
Verify Sketch version is 75 or higher. Test library feed functionality with known safe sources.📡 Detection & Monitoring
Log Indicators:
- Sketch downloading files without quarantine attributes
- Terminal.app launching from Sketch processes
Network Indicators:
- Sketch making unexpected network connections to download libraries
SIEM Query:
process_name:Sketch AND (network_connection OR file_download) AND NOT file_attribute:quarantine