CVE-2021-20700
📋 TL;DR
A buffer overflow vulnerability in NEC's Disk Agent component for CLUSTERPRO X and EXPRESSCLUSTER X allows remote attackers to execute arbitrary code via network communication. This affects Windows versions of these clustering products up to version 4.3. Organizations using these products for high-availability clustering are at risk.
💻 Affected Systems
- CLUSTERPRO X for Windows
- EXPRESSCLUSTER X for Windows
- CLUSTERPRO X SingleServerSafe for Windows
- EXPRESSCLUSTER X SingleServerSafe for Windows
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the cluster management system leading to full control over all cluster nodes, data exfiltration, and potential lateral movement across the enterprise network.
Likely Case
Remote code execution on the vulnerable cluster node, allowing attackers to disrupt cluster operations, steal sensitive data, or deploy ransomware.
If Mitigated
Limited impact if network segmentation prevents external access to cluster management interfaces and proper authentication controls are in place.
🎯 Exploit Status
The vulnerability requires no authentication and is remotely exploitable via network, making it relatively easy to exploit once details are known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 4.3 (specific version numbers in vendor advisory)
Vendor Advisory: https://jpn.nec.com/security-info/secinfo/nv21-015_en.html
Restart Required: Yes
Instructions:
1. Download the latest version from NEC's support portal. 2. Backup cluster configuration. 3. Apply the update following NEC's upgrade procedures. 4. Restart cluster services. 5. Verify cluster functionality.
🔧 Temporary Workarounds
Network Segmentation
windowsRestrict network access to cluster management interfaces using firewalls or network segmentation.
Windows Firewall: New-NetFirewallRule -DisplayName 'Block Cluster Management' -Direction Inbound -Protocol TCP -LocalPort [cluster_port] -Action Block
Disable Unnecessary Services
windowsDisable the Disk Agent service if not required for your cluster configuration.
sc stop "NEC Disk Agent"
sc config "NEC Disk Agent" start= disabled
🧯 If You Can't Patch
- Implement strict network segmentation to isolate cluster management interfaces from untrusted networks.
- Deploy intrusion detection systems to monitor for exploitation attempts against cluster services.
🔍 How to Verify
Check if Vulnerable:
Check installed version of CLUSTERPRO X or EXPRESSCLUSTER X via Control Panel > Programs and Features, or check NEC Disk Agent service version.Check Version:
wmic product where "name like '%CLUSTERPRO%' or name like '%EXPRESSCLUSTER%'" get name,versionVerify Fix Applied:
Verify version is updated beyond 4.3 and check that NEC Disk Agent service is running the patched version.📡 Detection & Monitoring
Log Indicators:
- Unusual network connections to cluster management ports
- Disk Agent service crashes or unexpected restarts
- Suspicious process creation from cluster services
Network Indicators:
- Unusual traffic patterns to cluster management ports (typically TCP 29000-29010)
- Buffer overflow patterns in network traffic to cluster services
SIEM Query:
source="windows" AND (event_id=4625 OR event_id=4688) AND process_name="*cluster*" OR destination_port IN (29000, 29001, 29002, 29003, 29004, 29005, 29006, 29007, 29008, 29009, 29010)