CVE-2021-21805
📋 TL;DR
This CVE describes a critical OS command injection vulnerability in Advantech R-SeeNet's ping.php script that allows unauthenticated attackers to execute arbitrary operating system commands on affected systems. Organizations using Advantech R-SeeNet version 2.4.12 (specifically the 20.10.2020 release) are affected. The vulnerability enables complete system compromise through remote code execution.
💻 Affected Systems
- Advantech R-SeeNet
📦 What is this software?
R Seenet by Advantech
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise leading to data theft, ransomware deployment, lateral movement within the network, and persistent backdoor installation.
Likely Case
Attacker gains shell access to the R-SeeNet server, potentially compromising the entire industrial control system monitoring infrastructure.
If Mitigated
With proper network segmentation and access controls, impact limited to the isolated R-SeeNet system only.
🎯 Exploit Status
The Talos Intelligence report includes technical details that could be easily weaponized. The vulnerability requires no authentication and simple HTTP requests.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 2.4.13 or later
Vendor Advisory: https://www.advantech.com/support/details/firmware?id=1-1S6V4S1
Restart Required: Yes
Instructions:
1. Download the latest version from Advantech's support portal. 2. Backup current configuration. 3. Install the update following vendor instructions. 4. Restart the R-SeeNet service. 5. Verify the ping.php functionality is properly sanitized.
🔧 Temporary Workarounds
Block access to ping.php
allTemporarily disable or restrict access to the vulnerable ping.php script
# For Apache: Add to .htaccess
<Files "ping.php">
Order allow,deny
Deny from all
</Files>
# For IIS: Use URL Rewrite to block /ping.php
Network segmentation
allIsolate R-SeeNet system from untrusted networks
# Example firewall rule (Linux iptables)
iptables -A INPUT -p tcp --dport 80 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit which systems can communicate with the R-SeeNet server
- Deploy a web application firewall (WAF) with command injection protection rules in front of the R-SeeNet system
🔍 How to Verify
Check if Vulnerable:
Check if ping.php accepts unsanitized parameters by testing with safe payloads like '127.0.0.1; echo test' (in a controlled environment only)Check Version:
Check the R-SeeNet web interface or configuration files for version information (typically in About or System Status sections)Verify Fix Applied:
After patching, test that ping.php properly validates and sanitizes input parameters and rejects command injection attempts📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests to ping.php with special characters (;, |, &, $)
- Multiple failed command execution attempts
- Unexpected system processes spawned from web server user
Network Indicators:
- HTTP POST/GET requests to /ping.php containing shell metacharacters
- Outbound connections from R-SeeNet server to suspicious external IPs
SIEM Query:
source="web_logs" AND (url="*ping.php*" AND (param="*;*" OR param="*|*" OR param="*&*" OR param="*$*"))