CVE-2021-20706 – This vulnerability allows remote attackers to u... (How to Fix)

Q: What is the severity of CVE-2021-20706?

CVE-2021-20706 has a CVSS score of 7.5 (HIGH). This vulnerability allows remote attackers to upload arbitrary files to affected NEC cluster management servers via network requests due to improper input validation. It affects NEC CLUSTERPRO X and EXPRESSCLUSTER X products running on Windows systems.

📋 TL;DR

This vulnerability allows remote attackers to upload arbitrary files to affected NEC cluster management servers via network requests due to improper input validation. It affects NEC CLUSTERPRO X and EXPRESSCLUSTER X products running on Windows systems.

💻 Affected Systems

Products:

CLUSTERPRO X
EXPRESSCLUSTER X
CLUSTERPRO X SingleServerSafe
EXPRESSCLUSTER X SingleServerSafe

Versions: 4.3 and earlier versions

Operating Systems: Windows

Default Config Vulnerable: ⚠️ Yes

Notes: Affects WebManager component specifically. All default installations are vulnerable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise through remote code execution, data theft, or ransomware deployment via malicious file uploads.

🟠

Likely Case

Unauthorized file upload leading to web shell installation, data exfiltration, or lateral movement within the network.

🟢

If Mitigated

Limited impact with proper network segmentation and file integrity monitoring detecting unauthorized uploads.

🌐 Internet-Facing: HIGH - Directly exposed web management interfaces allow remote exploitation without authentication.

🏢 Internal Only: MEDIUM - Internal attackers or compromised systems could exploit this for lateral movement.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Vulnerability allows remote file upload without authentication via network requests.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Versions after 4.3

Vendor Advisory: https://jpn.nec.com/security-info/secinfo/nv21-015_en.html

Restart Required: Yes

Instructions:

1. Download latest version from NEC support portal. 2. Backup configuration. 3. Install update following vendor documentation. 4. Restart cluster services.

🔧 Temporary Workarounds

Network Segmentation

all

Restrict access to WebManager interface to trusted management networks only.

Configure firewall rules to block external access to WebManager ports (typically 29003/TCP)

File Upload Restrictions

all

Implement web application firewall rules to block suspicious file upload patterns.

WAF rule: deny requests with file upload content to WebManager endpoints

🧯 If You Can't Patch

Implement strict network access controls to limit WebManager exposure
Deploy file integrity monitoring on WebManager directories

🔍 How to Verify

Check if Vulnerable:

Check WebManager version in administration interface or registry: HKEY_LOCAL_MACHINE\SOFTWARE\NEC\CLUSTERPRO\Version

Check Version:

reg query "HKLM\SOFTWARE\NEC\CLUSTERPRO" /v Version

Verify Fix Applied:

Verify version is greater than 4.3 and test file upload functionality is properly validated.

📡 Detection & Monitoring

Log Indicators:

Unusual file upload events in WebManager logs
Unexpected files in WebManager upload directories

Network Indicators:

HTTP POST requests with file uploads to WebManager endpoints
Unusual outbound connections from cluster nodes

SIEM Query:

source="webmanager.log" AND (event="file_upload" OR method="POST") AND NOT user="authorized_user"

📊 Metadata

CVE ID: CVE-2021-20706

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CWE: CWE-20

Published: November 3, 2021

Last Updated: November 21, 2024

🔗 References

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