Step-by-Step Guide to Detecting the DEEP#DOOR Python Backdoor

Introduction

The DEEP#DOOR Python backdoor is a sophisticated threat that uses tunneling services to steal browser and cloud credentials from compromised systems. This guide provides a step-by-step approach for security professionals to detect, analyze, and mitigate this stealthy framework. By following these steps, you can identify suspicious activity, block exfiltration channels, and remove persistent access mechanisms.

What You Need

• Access to compromised endpoints (or logs) with suspicious activity
• Windows Event Viewer or similar log analysis tool
• Process monitoring tool (e.g., Process Monitor, Sysmon)
• File integrity checker (e.g., PowerShell Get-FileHash)
• Network traffic analyzer (e.g., Wireshark, tcpdump)
• Python analysis environment (optional for script code review)
• Threat intelligence feeds for tunneling service domains
• Antivirus or EDR solution with real-time protection

Step-by-Step Detection and Mitigation

1. Step 1: Identify Initial Infection Vector

   The intrusion chain typically begins with execution of a batch script named install_obf.bat. This script disables Windows security controls (e.g., Windows Defender, firewall) and extracts the Python backdoor payload. Look for this filename in file systems, scheduled tasks, or startup registry keys. Use PowerShell to search for the script: Get-ChildItem -Path C:\ -Recurse -Filter 'install_obf.bat' -ErrorAction SilentlyContinue. Check recent file events for modifications.

2. Step 2: Analyze the Batch Script for Deobfuscation

   The script dynamically extracts the backdoor. Open install_obf.bat in a text editor and examine its contents. It likely contains encoded or obfuscated commands that decode and run a Python script. Log the decoded payload location—often a hidden directory like %APPDATA%\Microsoft\ or %TEMP%\. Document all extraction steps to understand the persistence mechanism.

3. Step 3: Locate the Python Backdoor Files

   After extraction, a Python script (e.g., svchost.py or chrome_updater.py) masquerades as a legitimate process. Search for Python files that are not part of official Python installations. Use file hashing to compare with known samples from threat intelligence. Also, look for accompanying configuration files (.config, .json) that may contain C2 server addresses.

4. Step 4: Examine Persistence Mechanisms

   DEEP#DOOR establishes persistence via scheduled tasks or registry run keys. Check Task Scheduler for tasks named after the backdoor (e.g., “WindowsUpdate” or “OneDriveSync”). Verify registry hives: HKLM\Software\Microsoft\Windows\CurrentVersion\Run and HKCU\...\Run. Remove any entries pointing to the malicious Python script.

5. Step 5: Monitor for Tunneling Service Connections

   The backdoor uses third-party tunneling services (like ngrok, LocalTunnel, or serveo) to bypass network restrictions. Analyze outbound connections to known tunneling domain patterns: *.ngrok.io, *.loca.lt, *.serveo.net. Use network monitoring tools to alert on these connections. Correlate with process names of the backdoor (e.g., python.exe or svchost.exe spawned from non-standard locations).

   

6. Step 6: Check for Credential Harvesting Activity

   The backdoor targets browser-stored credentials, cloud service tokens, and saved passwords. Inspect browser profile directories (e.g., %LOCALAPPDATA%\Google\Chrome\User Data\Default\Login Data) for unusual file access times. Use Sysmon Event ID 11 (FileCreate) to track modifications. Also, look for PowerShell commands that decrypt browser data (e.g., DPAPI calls) or access cloud configuration files like .aws/credentials or ~/.azure/accessTokens.json.

7. Step 7: Isolate and Remove the Backdoor
8. Once confirmed, isolate the affected machine from the network to prevent data exfiltration. Kill processes associated with the Python backdoor using taskkill /F /PID [PID]. Delete the extracted files and any scheduled tasks. Run a full antivirus scan and rotate all credentials stored on the device. Consider reimaging the system if persistence is deeply embedded.
9. Step 8: Verify Removal and Conduct Post-Mortem
10. After cleanup, monitor the system for 48 hours for any recurrent indicators. Check event logs for backdoor-related IDs (e.g., process creation events). Update detection rules in your SIEM to block similar patterns. Document the incident and share indicators of compromise (IOCs) with relevant stakeholders.

Tips

• Always test detection steps in a sandbox environment before deploying to production.
• Use threat intelligence sources to update blocks for tunneling service domains regularly.
• Enable Windows Event Logging for process creation (Event ID 4688) and command line auditing to capture batch script execution.
• Educate users about phishing emails that may deliver install_obf.bat as an attachment.
• Implement application whitelisting to prevent unsigned Python scripts from running.
• If you suspect credential theft, immediately reset passwords and revoke cloud API keys.