CVE-2021-42976
📋 TL;DR
A buffer overflow vulnerability in NoMachine Enterprise Desktop allows local attackers to execute arbitrary code with kernel privileges or cause denial of service via memory corruption. This affects users running NoMachine Enterprise Desktop versions 4.0.346 through 7.7.4. Attackers need local access to exploit this vulnerability.
💻 Affected Systems
- NoMachine Enterprise Desktop
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via kernel-mode arbitrary code execution leading to full administrative control, data theft, and persistent backdoor installation.
Likely Case
Privilege escalation from a standard user to SYSTEM/root level, enabling lateral movement, credential harvesting, and installation of additional malware.
If Mitigated
Limited impact if proper access controls prevent local attackers from reaching vulnerable systems, though denial of service could still occur.
🎯 Exploit Status
Requires local access and knowledge of IOCTL manipulation. The vulnerability is in a widely used component that could be targeted by sophisticated attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 7.7.4 and later
Vendor Advisory: https://www.nomachine.com/
Restart Required: Yes
Instructions:
1. Download NoMachine Enterprise Desktop version 7.7.4 or later from the official website. 2. Install the update following standard installation procedures. 3. Restart the system to ensure all components are properly loaded.
🔧 Temporary Workarounds
Disable USB-over-Ethernet functionality
allRemove or restrict access to the vulnerable IOCTL handler by disabling USB-over-Ethernet features
Specific commands depend on OS and configuration - consult NoMachine documentation
Restrict local user access
allImplement strict access controls to prevent untrusted users from accessing systems running NoMachine
🧯 If You Can't Patch
- Implement strict principle of least privilege and limit local user access to vulnerable systems
- Monitor for unusual process creation or privilege escalation attempts using endpoint detection tools
🔍 How to Verify
Check if Vulnerable:
Check NoMachine version via the application interface or by examining installed software version. Vulnerable if version is between 4.0.346 and 7.7.4.Check Version:
On Windows: Check Programs and Features. On Linux: 'nomachine --version' or check package manager. On macOS: Check About NoMachine in application menu.Verify Fix Applied:
Verify NoMachine version is 7.7.4 or later through the application interface or system software inventory.📡 Detection & Monitoring
Log Indicators:
- Unusual process creation with SYSTEM privileges
- Failed attempts to access restricted kernel memory areas
- Crash logs from NoMachine service
Network Indicators:
- Unusual local network traffic from NoMachine processes
- Attempts to access USB-over-Ethernet components
SIEM Query:
Process Creation where Parent Process contains 'nomachine' AND Integrity Level changes to SYSTEM