CVE-2021-21804
📋 TL;DR
This CVE describes a local file inclusion vulnerability in Advantech R-SeeNet's options.php script that allows attackers to execute arbitrary PHP code via crafted HTTP requests. Organizations using Advantech R-SeeNet version 2.4.12 (specifically the 20.10.2020 release) are affected. The vulnerability enables remote code execution with potentially severe consequences.
💻 Affected Systems
- Advantech R-SeeNet
📦 What is this software?
R Seenet by Advantech
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, install malware, exfiltrate sensitive data, and pivot to other network systems.
Likely Case
Unauthorized access to the R-SeeNet system leading to data theft, system manipulation, and potential lateral movement within the network.
If Mitigated
Limited impact due to network segmentation, proper access controls, and monitoring that detects exploitation attempts.
🎯 Exploit Status
The vulnerability requires sending crafted HTTP requests to the options.php endpoint; exploitation details are publicly available in the Talos Intelligence reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check with Advantech for updated version
Vendor Advisory: https://www.advantech.com/support
Restart Required: Yes
Instructions:
1. Contact Advantech support for patch availability. 2. Backup current configuration. 3. Apply the provided patch. 4. Restart the R-SeeNet service. 5. Verify functionality.
🔧 Temporary Workarounds
Restrict Access to options.php
allBlock or restrict HTTP access to the vulnerable options.php script using web server configuration or network controls.
# For Apache: Add to .htaccess or httpd.conf
<Files "options.php">
Order Deny,Allow
Deny from all
</Files>
# For Nginx: Add to server block
location ~ /options\.php$ {
deny all;
return 403;
}
Network Segmentation
linuxIsolate R-SeeNet systems from untrusted networks and implement strict firewall rules.
# Example iptables rule to restrict access
# 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 who can reach the R-SeeNet web interface
- Deploy web application firewall (WAF) rules to block LFI exploitation patterns
🔍 How to Verify
Check if Vulnerable:
Check if R-SeeNet version is 2.4.12 (20.10.2020) via web interface or system documentation; test with controlled exploitation attempt in isolated environment.Check Version:
Check web interface or consult system documentation; no universal command available.Verify Fix Applied:
Verify version is updated beyond 2.4.12 (20.10.2020); test that crafted requests to options.php no longer execute arbitrary code.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests to options.php with file inclusion parameters
- PHP error logs showing file inclusion attempts
- Web server logs with suspicious patterns to vulnerable endpoint
Network Indicators:
- HTTP traffic to options.php with unusual parameters
- Multiple failed exploitation attempts from single source
SIEM Query:
source="web_server_logs" AND uri="*options.php*" AND (param="*../*" OR param="*php://*" OR param="*file=*")