These scripts are designed to make it easy and straight-forward to configure a Ubuntu virtual machine to act as a PPTP VPN endpoint, and forward traffic to your favorite web proxy or other tool. I personally use this for doing mobile testing, as both Android and iOS support PPTP VPNs out of the box.
Note: There is no black magic here - simply some utilities to make it easier to use.
The typical work flow would be a VM that has one interface, we'll call it 'eth0'. First, we start the pptpd daemon and then we configure IP forwarding and apply custom iptables rules to forward traffic to specific proxies, such as Burp.
This tool is designed to work on Ubuntu virtual machines operating in 'bridged' mode. Your mileage will vary if you use another VM, but I suppose Kali Linux should also work fine.
To download and setup the tool, run the following commands:
$ git clone https://github.com/jakev/mitm-helper-vpn
$ cd mitm-helper-vpn
$ sudo ./install_dependencies.sh
$ sudo dpkg -i build/mitm-helper-vpn_0.1.deb
First, we need to add a user. This example will add a user called 'analyst', with a password of 'analyst':
$ sudo mitm-pptp-users add analyst analyst
If you want to see your current users:
$ sudo mitm-pptp-users list
To delete a user:
$ sudo mitm-pptp-users del analyst
To delete all users:
$ sudo mitm-pptp-users purge
The file /etc/mitm-pptp.conf will be used to configure how you will intercept traffic. By default, traffic is simply passed through (no proxy). This should work if you just want to observe traffic using a tool like Wireshark. In our case, let's assume we have Burp running on port 9999, and we'd like to forward traffic on ports 80 and 443 to this proxy. We configure the /etc/mitm-pptp.conf file as follows:
[HTTP Proxies]
ProxyPort:9999
ForwardPorts:80,443
Now, let's say that we determine our app/device uses a custom protocol on port 1234, and Burp is not useful for intercepting this traffic. We created a python script, and it is listening on port 8888. Let's add rules for this:
[HTTP Proxies]
ProxyPort:9999
ForwardPorts:80,443
[Binary Coolness Proxy]
ProxyPort:8888
ForwardPorts:1234
This configuration can be found in the file sample.mitm-pptp.conf.
Side note for Burp users: You'll likely need to listen on all interfaces AND enable the invisible proxying to have your setup work properly.
By default, the PPTP server will be disabled and no forwarding will happen. Once you're ready to start, run:
$ sudo mitm-pptp -v
If you want to specify a custom configuration file, you can do so with the -c argument:
$ sudo mitm-pptp -v -c my-pptp.conf
By hitting Ctrl+C, the script will begin the shutdown process.