Spikefish Solutions Blog

• PAM
• https://github.com/google/google-authenticator
• Free Radius
• Google Authentication App. ( iOS, Android, Chrome, etc )

Request comes into the firewall in the following form

username

unix passwd password + OTP

1. Firewall forwards request to Free Radius (which is installed on the 750 in this case).
2. Free Radius passes the username and password to via the Radius PAM module.
3. PAM passes the username and password to the Google LibPAM module. 
4. Google's libpam module strips the OTP off the password string and verifies the OTP with google. If the authentication is good Google's libpam sends the password (without the OTP) string back to pam.
5. Pam then checks the password using the normal unix checks.

If everything is good the FreeRadius sends an accept message back to the firewall and then you're golden!

Now before we get too much further into this let me give you a little warning. This will require some hacking. Why is that you ask? Well.. Kali (guessing most if not all Debian based OSes) assumes the Linux kernel has audit support enabled but the kernel on the 750 does not as seen by

This causes Google's pam module to fail when creating a network connection. Found this with strace. Basically you'll see socket(bla NETLINK_ADUIT) error =PROTOUNSUPPORTED or something like that.

There might be a better way of dealing with this, but the current work around is to recompile the pam package. What is kind of a pain is if there is an update to pam and you update the chroot with say apt-get upgrade or something then you'll need to recompile the package with the new pam module. You can always make more then one chroot also so you could make one just for Free Radius and a different one for all the things Kali can do.

Right so anyway... Let configure some stuff. I'm going to assume you already have the chroot setup so i'll be going right into that, but first add a loop interface. This will be a private interface we'll be telling freeraidus to use. You should also create 2 firewall rules for this under the "Incoming, Internal and VPN traffic" section. One to allow radius from loop00 to loop00 and a second rule to deny all other radius. BTW radius object has a timeout of 3600 seconds (seems high for udp) so if you've already passed traffic the deny rule won't take effect until radius falls out of the connections table. I lowered radius timeout to 30 seconds. ok ok ok.. configure stuff.

From clish run the following to create a loop interface for radius.

Next we'll login to the chroot and update the apt-get system then install some packages (FreeRadius, Google libpam). BTW make sure proc and sys are mounted inside the chroot. I updated the kali write up about that.

A lot of things will start download. Lets queue up some Music while we wait.

After a few minutes you'll have almost everything you need. 

############

# Start hacking
############

# This part is only needed for installing on the 750. If you're by chance running through this for an external radius server you can skip this.

So now we have all our apps installed. Lets rebuild pam! 

First you'll need to tell apt you'll be downloading source. If your not sure how to change /etc/apt/source.list basically just copy whats there and change the starting 'deb' to 'deb-src'. This will do that for you if you super lazy. We'll also be installing everything needed to build pam.

ok all done /pam you can delete this entire dir if you want.

###########
# End hacking
###########

Ok right.. so lets configure everything!

###########
# Start Radius config!
###########

Edit /etc/pam.d/radiusd. This is what we want it to look like. This is so the user FreeRadius runs as can read the users Google authenticator configuration file.


/etc/freeradius/3.0/clients



Now lets edit the main site radius server config.

/etc/freeradius/3.0/sites-enabled/default

replace all

with


Comment out ALL the IPv6 sections (the entire section)

uncomment the pam section (around line 489)

edit

/etc/freeradius/3.0/proxy.conf

uncomment src_ip and set it to the loop00 interface IP as well.



Geez.. are we done yet? As it turns out.. almost! We're now going to make the FreeRadius server run as root. This is needed because the google pam module will switch to the user's uid before reading the config file. I did try the pam option to allow perms 0660 but because of the uid switch I couldn't get it to work.

edit

/etc/freeradius/3.0/radiusd.conf

and change user and group to root.



First add a unix user. This will be the user account you configure for the VPN. I'll make a testuser account. Afterwards log as test user and setup google-authenticator. BTW you might want to full size your ssh session so you can see the full QRcode on the console (yes that work.. amamzing).

Answer yes to all questions, open the app and take a pic of the QRcode with the app (i used iOS version). This will fully configure the OTP app. Side note.. that is so cool..

###########

# End of google config

###########

OK, lets fire it up!

logout of the chroot jail and start the radius server.

##########
# Firewall config (ok well I created the loop00 interface way above but firewall config!)
##########

Now to wrap everything up, make your firewall rules look like this.

########

# If something goes wrong!

########

Most the the problems I were with the radius configs. If you want to debug radius run it with the -XXX arguments and you'll get a decent amount of debug output. It can also be useful to start rsyslog inside the chroot for more log. Also the google pam module has a debug option. Follow the link at the top for more info. In addition you can add the word "debug" to the pam_google_authenticator.so line in /etc/pam.d/radiusd file. This will spit out helpful into on what Google Authenticator is doing. Make sure NTP is enabled and that the clock is synced. If not you'll have to sync the clock and possibly recreate the token.