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So I'm using WPA2-EAP for a few years now with FreeRadius server. And it's pretty okay, I mean I don't really consider wifi access to be so super-duper critical break in success because it's pretty restricted anyways on other levels so I accepted any potential risk (which is still significantly lower than PSK). But I always wondered... How about server or workstation authentication? How secure RADIUS client <> server connection really is and how easy it is to deploy rogue RADIUS server authenticating everyone to everything?

Let's focus on 2 scenarios that come to my mind first:

  1. Evil dude connecting between server and radius server:

    [server] -> [switch] -> [evil dude] -> [switch] -> [RADIUS server]

  2. User workstation outside of company network with disabled VPN:

    [workstation] -> [dodgy hotspot] -> [evil dude]

Questions are following: Is in 1st case possible to inject rogue RADIUS allowing access to server with credentials like root:abc123?

Is 2nd case equivalent to workstation having no user credentials and unrestricted admin access? What is necessary to deploy rogue RADIUS and can it be mitigated by hardening auth between RADIUS server and client?

I don't consider accessing data available on RADIUS server real issue because if someone has access to it then it's game over anyways. But I'm a bit concerned about security of using secret for RADIUS client <> server connection and I'm not sure if it's valid concern from exploitation point of view. Always certificates made me more confident in this field than PSK.

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If it helps you feel better, 99% of our encrypted communication uses symmetric cryptography (Like PSKs). We only use asymmetric cryptography (Certificates) to transfer symmetric keys and sign hashes.

Situation 1 is completely possible under three conditions:

  1. The "evil dude" has presence on the network between the two switches (In most cases, to pull this off, he would actually have to be between them, and using a MITM

  2. He would already have to have compromised the PSK(Not a simple feat, and if he was capable of pulling that off, he could probably have done worse while he was at it.)

  3. Your RADIUS server authenticates with an insecure protocol.

If your RADIUS server authenticates with certificate based encryption, then even if they pull off 1 and 2, they'd also need the private key from the authentication server to pull off the MITM.

So, technically possible, but if your keys are compromised, you have bigger problems anyway.

Situation 2 is one of the reasons we have VPNs in the first place. Consider an Always-on VPN to mitigate the risk from leaving the VPN off, and NEVER EVER EVER click through to a web page that flags your browser's security feature.

Unsafe means UNSAFE.

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  • 1) doesn't sound difficult if evil dude has federal search warrant. I was concerned about situation where evil dude can pull out cable from switch and plug through middleware or just connect straight to own server. Even though physical access sounds quite terrible in the first place, if all drives have full encryption and TTY has no autologin I believe it's quite hard to authenticate into such machine without crazy stuff like cold boot. Especially if we have disabled USB. I wonder whether using RADIUS could allow attacker with physical access to such machine to bypass authentication.
    – Lapsio
    Mar 24, 2018 at 20:14
  • But is it possible to use FreeRADIUS with certificate based client authentication? I can only see articles about certificate based user auth, not client as RADIUS client software.
    – Lapsio
    Mar 24, 2018 at 20:17
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    As a basic rule of information security, if an attacker has physical access to your machine, it is no longer your machine.
    – Andrew Hendrix
    Mar 24, 2018 at 20:17
  • RADIUS is simply a protocol that allows edge devices to pass authentication authorization and accounting load off to another server capable of handling that. This is important because the RADIUS enabled edge device does not perform the actual authentication. It simply acts as a proxy to the real authenticator using whatever method you want. If the client has a means of sending a message that only the authenticator can open, the edge device can only pass it along.
    – Andrew Hendrix
    Mar 24, 2018 at 20:23

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