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Stealing MFA/2FA tokens and using them to logon with VPN clients
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README.md
VPN Login.xaml
login.php
mfastealer.go

README.md

mfastealer

This project includes sample code to help those wanting to use UiPath (RPA) to get around MFA/2FA VPN configurations. For more background information, see https://adapt-and-attack.com/2018/06/04/defeating-2fa-with-robots/

What You Need

How's It Work?

Target is phished to enter credentials on a phishing page, including their MFA/2FA token(s). The phishing page captures the creds, sends them down an SSH tunnel to an attacker's Windows system. The mfastealer.exe Go script works as an intermediary tool to receive the captured crednetials and write them to a file. UiPath, which is a Robotic Process Automation (RPA) tool, will notice the file was updated with credentials, and will open the VPN client, enter in all credentials, and initiate the VPN connection.

This entire process is fast enough (~5 seconds) to capture the credentials + token(s) and initiate the connection before the token(s) would typically expire. Obviously this is very dependent on the target infrastructure and VPN configuration.

Setup

This is probably pretty new to most people, so if you have questions feel free to DM me on Twitter (@leoloobeek) or on the BloodHoundGang slack (@leo).

UiPath

Install the UiPath Community Edition. You can then import the VPN Login.xaml file to get started, this saved project is for AnyConnect. I can't promise this will work for all AnyConnect clients and configurations, and definitely will not work for other VPN clients.

I'm absolutely no expert on UiPath and basically just fiddled with it until it worked for my needs. I would say it is pretty intuitive and if you run into any issues hit me up. Few things to get you started:

  • Import the provided VPN Login.xaml file to see what I used for the video demo
  • You will need to setup a File change trigger to watch when the loginFile.txt is written to. This file will be in the same directory as mfastealer.exe. The mfastealer.exe tool will write username, password and token on each line of loginFile.txt.
  • Either 'hardcode' or request the full path to the directory mfastealer.exe is in. This will allow you to run mfastealer.exe and easily find the loginFile.txt that mfastealer.exe will write to
  • Start up the VPN client either at the beginning with UiPath or yourself to save on time

As you'll see in the provided UiPath VPN Login.xaml file, I used a lot of On Element Appear, Find Window and Attach Window when interacting with the VPN GUI client. That seemed to work reliably for me, but there are plenty of ways to accomplish. You may need to play around with it for 20 minutes or so to get the hang of it.

The provided demo UiPath project DOES NOT handle errors. A useful addition would be to detect if the VPN connection failed due to the target fatfingering their password, then clearing out the loginFile.txt file awaiting for another target to fall for the attack.

mfastealer.exe

Next, download either the mfastealer.exe binary from the Releases page or compile it to run on Windows. Running the binary should start a webserver listening on the provied port. This webserver is expecting to receive an HTTP POST request with username, password, and secondPassword. On the first set of credentials received, mfastealer.exe will write the credentials to loginFile.txt and to cred.log. All subsequent credentials received will just be written to cred.log for safe keeping.

Example: mfastealer.exe 3000

Phishing Page Setup

The attacker will setup a phishing page with a form requesting the username, password, and second password (token, "push", etc.). The page should then send these credentials as username, password, and secondPassword respectively to the included login.php page. Setup a local SSH port forward from your Windows system running mfastealer.exe and UiPath to the webserver. You will need to forward the local system TCP port 3000 to the webserver's localhost:3000. Then the login.php file should post credentials to localhost:3000, which should send the credentials down to mfastealer.exe. Once that happens, UiPath should pick up the rest of the work!

Special Thanks

Thanks to the guys over at FireEye for their ReelPhish blog post and tool release. The login.php file along with the overall idea of stealing tokens, came directly from that tool.

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