| name | hunting-for-webshells-in-web-servers |
| description | Detect webshells planted on web servers by scanning for high-entropy files, suspicious PHP/JSP/ASP patterns (eval, base64_decode, system, passthru), recently modified files in web roots, and anomalous file sizes. Uses Shannon entropy calculation to flag obfuscated payloads and regex pattern matching against known webshell signatures. |
| domain | cybersecurity |
| subdomain | security-operations |
| tags | ["hunting","for","webshells","web"] |
| version | 1.0 |
| author | mahipal |
| license | Apache-2.0 |
Instructions
- Install dependencies:
pip install yara-python
- Identify web server document roots to scan (e.g.,
/var/www/html, /opt/lampp/htdocs).
- Run the agent to scan for webshells:
- Shannon entropy analysis flags files with entropy > 5.5
- Pattern matching detects eval(), base64_decode(), system(), passthru(), shell_exec()
- File modification time analysis finds recently changed files
- Extension filtering targets .php, .jsp, .asp, .aspx, .cgi, .py files
python scripts/agent.py --webroot /var/www/html --output webshell_report.json
Examples
High-Entropy PHP Webshell Detection
File: /var/www/html/uploads/img_thumb.php
Entropy: 6.12 (threshold: 5.5)
Patterns matched: eval(), base64_decode(), str_rot13()
Last modified: 2025-12-01 03:42:00 (outside business hours)
Verdict: SUSPICIOUS - likely obfuscated webshell
