CVE-2021-35062
📋 TL;DR
CVE-2021-35062 is a shell command injection vulnerability in the DRK Odenwaldkreis Testerfassung COVID-19 test result system. Attackers with a valid test result token can execute arbitrary shell commands with web server privileges. This affects organizations using the March-2021 version of this specific COVID-19 test management software.
💻 Affected Systems
- DRK Odenwaldkreis Testerfassung
📦 What is this software?
Testerfassung by Testzentrum Odw
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise leading to data exfiltration, ransomware deployment, or use as pivot point into internal networks.
Likely Case
Unauthorized access to sensitive health data, modification of test results, or installation of cryptocurrency miners.
If Mitigated
Limited impact with proper network segmentation, minimal web server privileges, and command execution restrictions.
🎯 Exploit Status
Exploitation requires a valid test token but is straightforward once obtained. GitHub references contain technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Post-March-2021 versions
Vendor Advisory: No formal vendor advisory found. Community disclosure via GitHub.
Restart Required: No
Instructions:
1. Update to latest version of DRK Odenwaldkreis Testerfassung. 2. If source code available, sanitize user input in result.php using proper escaping functions. 3. Replace shell command execution with safer alternatives.
🔧 Temporary Workarounds
Input Validation and Sanitization
linuxAdd input validation to filter shell metacharacters before processing in result.php
# Example PHP sanitization: $input = escapeshellarg($_GET['parameter']);
Web Application Firewall Rules
allBlock requests containing shell metacharacters targeting result.php
# ModSecurity rule: SecRule ARGS "[;|&`$()]" "id:1001,phase:2,deny"
🧯 If You Can't Patch
- Network segmentation: Isolate the system from critical infrastructure and limit outbound connections.
- Implement strict access controls: Restrict access to result.php to authorized IPs only via web server configuration.
🔍 How to Verify
Check if Vulnerable:
Review result.php source code for unsanitized user input passed to shell_exec(), system(), or similar functions.Check Version:
# Check software version: grep -r 'version\|Version' /path/to/application/ | head -5Verify Fix Applied:
Test with controlled input containing shell metacharacters (e.g., ; ls) and verify no command execution occurs.📡 Detection & Monitoring
Log Indicators:
- Unusual shell commands in web server logs
- Multiple failed access attempts to result.php with special characters
Network Indicators:
- Unexpected outbound connections from web server
- Traffic to suspicious IPs/domains
SIEM Query:
source="web_server" AND uri="*result.php*" AND (query="*;*" OR query="*|*" OR query="*`*" OR query="*$(*")