Defending Against China-Nexus Covert Networks: Edge Router Compromise & Detection

---
title: Potential Cisco IOS XE Webshell Implantation Activity
id: 88f4d321-5a6b-4c7d-9e1f-2b3c4d5e6f78
status: experimental
description: Detects potential webshell implantation or exploitation attempts on Cisco IOS XE devices targeting specific paths associated with CVE-2023-20198.
references:
  - https://www.cisa.gov/known-exploited-vulnerabilities-catalog
author: Security Arsenal
date: 2024/05/20
tags:
  - attack.initial_access
  - attack.t1190
logsource:
  category: webserver
  product: apache
  # Note: Adjust product based on your router's logging format (nginx, cisco-asa, etc.)
detection:
  selection:
  # Cisco IOS XE exploitation often utilizes the /webui or /% path segments
    c-uri|contains:
      - '/%%/'
      - '/webui/'
      - '/admin/'
  filter:
    c-sc-status|startswith:
      - '40'
      - '50' # Looking for failures indicating exploit attempts, or 200s indicating success
  condition: selection
falsepositives:
  - Legitimate administrative access from internal subnets
level: high
---
title: Netgear ProSafe RCE Exploitation Attempt
id: 99a1e432-6b7c-5d8e-0f2a-3c4d5e6f7a89
status: experimental
description: Detects exploitation attempts against Netgear ProSafe devices leveraging the setup.cgi vulnerability (CVE-2023-20026).
references:
  - https://www.cisa.gov/known-exploited-vulnerabilities-catalog
author: Security Arsenal
date: 2024/05/20
tags:
  - attack.initial_access
  - attack.t1190
logsource:
  category: webserver
  product: netgear
detection:
  selection:
    c-uri|contains: 'setup.cgi'
    c-uri|contains:
      - 'CMD='
      - 'download_file='
      - 'remote_file='
  condition: selection
falsepositives:
  - Legitimate administrative configuration changes
level: critical
---
title: Suspicious User-Agent - China-Nexus Scanner
id: 10b2f543-7c8d-6e9f-1a3b-4d5e6f7a8b90
status: experimental
description: Detects scanning activity associated with China-nexus actors utilizing specific scripting user agents or empty strings on edge infrastructure.
references:
  - https://attack.mitre.org/groups/G0128/
author: Security Arsenal
date: 2024/05/20
tags:
  - attack.reconnaissance
  - attack.t1590
logsource:
  category: webserver
detection:
  selection:
    cs-user-agent|contains:
      - 'python-requests'
      - 'Hello, world'
      - 'masscan'
  condition: selection
falsepositives:
  - Legitimate monitoring tools
level: medium

// Hunt for Cisco IOS XE Webshell Implantation Paths (CVE-2023-20198)
// Map to your specific Syslog or DeviceEvents tables
Syslog
| where Facility in ('Cisco', 'IOS')
| where SyslogMessage has_any ('/%', '/webui', '/system/file')
| extend RequestPath = extract(@'GET\s+(/[\S]+)', 1, SyslogMessage)
| where RequestPath has '%' or RequestPath has 'webui'
| project TimeGenerated, Computer, SourceIP, RequestPath, SyslogMessage
| summarize count() by SourceIP, RequestPath, bin(TimeGenerated, 5m)
| where count_ > 5


// Hunt for Netgear and DrayTek Exploitation Attempts
CommonSecurityLog
| where DeviceVendor in ('Netgear', 'DrayTek')
| where RequestURL contains "setup.cgi" or RequestURL contains "apply.cgi"
| where RequestURL contains "CMD=" or RequestURL contains "download_file="
| project TimeGenerated, DeviceName, SourceIP, DestinationPort, RequestURL, Activity
| sort by TimeGenerated desc


// Hunt for Successful Logins from Geographically Suspicious Locations on Edge Devices
SigninLogs
| where AppDisplayName contains "Cisco" or AppDisplayName contains "VPN"
| where ResultDescription == "Success"
| project TimeGenerated, UserPrincipalName, IPAddress, Location, AppDisplayName
| evaluate geoip_lookup(IPAddress)
| where Country in ("China", "Russia", "North Korea", "Iran") // Adjust based on your risk profile
| sort by TimeGenerated desc

-- Hunt for suspicious persistence on Linux-based edge devices
SELECT 
  Sys.Username,
  Sys.Path,
  Sys.Mode.String AS Mode,
  Sys.Size,
  Sys.ModTime
FROM glob(globs='/etc/cron.*/*', root='/')
WHERE Sys.Mode.String =~ 'rw.*'
   -- Look for obfuscated names or recent modifications
   AND (ModTime > now() - 7h OR Path =~ '.*\.(sh|py|bin)$')
UNION ALL
SELECT 
  Sys.Username,
  Sys.Path,
  Sys.ModTime
FROM glob(globs='/home/*/.ssh/authorized_keys', root='/')
WHERE Sys.ModTime > now() - 24h

#!/bin/bash
# Remediation/Hardening Script for Compromised Edge Infrastructure
# Run with elevated privileges

echo "[*] Starting Security Arsenal - Edge Device Hardening Check..."

# 1. Check for suspicious webshell artifacts (common paths)
echo "[+] Checking for common webshell paths..."
WEB_ROOTS=("/var/www/html" "/usr/local/www" "/www" "/opt/cisco/ncs/current/webui")

for dir in "${WEB_ROOTS[@]}"; do
  if [ -d "$dir" ]; then
    echo "[*] Scanning $dir for suspicious patterns..."
    # Look for files with 'system', 'passthru', 'eval' often found in PHP shells
    find "$dir" -type f -name "*.php" -exec grep -l "eval(base64_decode" {} \; 2>/dev/null
    # Look for the specific Cisco webshell artifact path if accessible
    if [ -f "$dir/%%" ] || [ -f "$dir/.component" ]; then
      echo "[!] ALERT: Potential webshell artifact found in $dir"
    fi
  fi
done

# 2. Verify Management Interface Security
echo "[+] Verifying Management Interface status..."
# Check if HTTP (80) is listening on external interfaces (simplified check)
if netstat -tuln | grep -E ':80\s' | grep '0.0.0.0'; then
  echo "[!] WARNING: HTTP (Port 80) is listening on all interfaces. Recommend disabling HTTP and enforcing HTTPS only."
fi

# 3. Check for default credentials or weak users (Shadow file check example)
echo "[+] Checking for empty password fields..."
if grep -E '^.+::' /etc/shadow; then
  echo "[!] CRITICAL: Users with empty passwords detected."
fi

echo "[*] Script complete. Please review output and patch devices per vendor advisories."