CVE-2021-1751
📋 TL;DR
This vulnerability allows attackers to execute arbitrary code on macOS systems by tricking users into mounting a malicious Samba network share. It affects macOS Mojave, Catalina, and Big Sur versions before specific security updates. The attack requires user interaction to mount the malicious share.
💻 Affected Systems
- macOS
📦 What is this software?
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 with root privileges, allowing data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Limited compromise of the user account that mounted the share, potentially leading to data exfiltration or lateral movement within the network.
If Mitigated
No impact if users avoid mounting untrusted Samba shares and systems are fully patched.
🎯 Exploit Status
Requires user interaction to mount malicious share. No public exploit code has been disclosed as of knowledge cutoff.
🛠️ 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 security updates. 3. Restart your Mac when prompted.
🔧 Temporary Workarounds
Disable SMB mounting
allPrevent mounting of Samba/SMB network shares through system configuration
sudo defaults write /Library/Preferences/com.apple.desktopservices DSDontWriteNetworkStores -bool TRUE
User awareness training
allEducate users to only mount trusted network shares from known sources
🧯 If You Can't Patch
- Implement network segmentation to restrict SMB traffic to trusted servers only
- Use application control to block execution of unknown binaries from network locations
🔍 How to Verify
Check if Vulnerable:
Check macOS version: if running Mojave, Catalina, or Big Sur without the specified security updates, system is vulnerable.Check Version:
sw_versVerify Fix Applied:
Verify macOS version matches patched versions: Big Sur 11.2+, or check that Security Update 2021-001 is installed for Catalina/Mojave.📡 Detection & Monitoring
Log Indicators:
- Unusual SMB mount events in system logs
- Process execution from network-mounted volumes
Network Indicators:
- Unexpected SMB connections to untrusted IP addresses
- SMB traffic to non-standard ports
SIEM Query:
source="macos_system_logs" AND (event="mount" OR event="smb") AND dest_ip NOT IN [trusted_ips]