SOPHOS UTM: Use Azure MFA for SSLVPN and Userportal

Inspiration for this post was taken from: https://rieskaniemi.com/azuremfa-nps-extension-with-sophos-utm-firewall/

Some of the things that I’ve seen at work, is that Sophos UTM VPN users are using one token for Sophos SSLVPN and another for ex. Office 365 services. Both tokens can be in Microsoft Authenticator, but only the one that Office 365 is using, can do the “pop-up”, letting the user easy sign-in, like this:

Microsoft Authenticator beta app for iOS and Android updated with ...

Nonetheless it’s easier for the IT dept. (and the user!) to maintain only one token solution πŸ™‚

Here is the auth flow for Azure MFA with NPS Extension:

Nice isn’t it πŸ˜‰

So how to fix?

We setup Sophos UTM for RADIUS validation for SSLVPN and UserPortal access, and if you use the built-in OTP solution, disable that πŸ™‚

To get started:

  • If you do not have MFA enabled for your Office 365/Azure AD account’s you can enable it through following link: https://aka.ms/mfasetup
  • And of course you need to have set Azure AD Connect to get your on-premise talking with Azure, I will not go into the details with this here, as I assume this is already setup and working πŸ™‚

Let’s go:

  1. Install the Network Policy Server (NPS) role on your member server or domain controller. Refering to the Network Policy Server Best Practices, then you will find this “To optimize NPS authentication and authorization response times and minimize network traffic, install NPS on a domain controller.” So we will go ahead and place this on the domain controller, but remember it’s also possible to do it on a domain joined member server!
    Press “Next” and the installation begins:
  2. After installation has ended, go and join the NPS to the Active Directory, right-click NPS (Local):

  3. Download and install the NPS Extension for Azure MFA here:
    https://www.microsoft.com/en-us/download/details.aspx?id=54688Note: As i did try this on a server with already setup NPS, it failed with the other mechanisms, because of this:
    https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-nps-extension#control-radius-clients-that-require-mfa

    β€œ

    Control RADIUS clients that require MFA

    Once you enable MFA for a RADIUS client using the NPS extension, all authentications for this client are required to perform MFA. If you want to enable MFA for some RADIUS clients but not others, you can configure two NPS servers and install the extension on only one of them.

    Configure RADIUS clients that you want to require MFA to send requests to the NPS server configured with the extension, and other RADIUS clients to the NPS server not configured with the extension.”

    So the β€œworkround” is to run the MFA for the Sophos on a seprate NPS instanceΒ πŸ™‚

  4. After it’s installed, go and follow the configure is like it’s stated here (Find TenantID and run Powershell script):
    https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-nps-extension#azure-active-directory
  5. Go and configure your radius Client, here it’s the UTM:


    Remember the secret, we need it later on πŸ™‚

  6. Create a “Connection request policy”:

    See above the NAS Identifier, it’s “ssl”, it’s taken from this scheme:


    Found here: https://community.sophos.com/kb/en-us/116144

    Just set like above, and the rest of the settings, just leave them to their defaults πŸ™‚

  7. Now create a “Network Policy”
    Add a domain group, that shall have this access, to simplify, here I have choose domain\Domain Users
    Now the EAP types, UTM does only support PAP, as far as I have tested:


    You will get a warning telling you that you have choosen unencrypted auth (locally – not on the Internet!), just press OK.
    Just left the rest to their default’s and save the policy.

  8. Now to create a firewall rule:

  9. Now to setup the UTM for this:

    Add new Authentication server:

    Remember to choose RADIUS:


    Fill in as your environment matches:

    Type in the secret you wrote down earlier and create a host object for your NPS, also remember to change the timeout from 3 to 15 secs!

    You can now test is the authentication through NPS and Azure MFA is working, change NAS-Identifier to “ssl” type in a users username (e.mail adress) and password, and your phone should pop-up with Microsoft Authenticator πŸ™‚

  10. Now to grant the RADIUS users access to SSL-VPN

    Just add the built-in object “Radius Users” to your SSL-VPN profile:

  11. Now login to the User Portal and download a VPN client (You cannot use the old ones, if you already had thoose installed)
  12. Now connect through VPN, type in your full email in username and your password, then wait for MS Authenticator to pop-up, accept the token and you are logged into VPN πŸ™‚

Sources:

https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-nps-extension-vpn

https://docs.microsoft.com/en-us/windows-server/networking/technologies/nps/nps-best-practices

10 Comments

  1. Thorsten Sult

    Great job, thank you very much.

    Reply
    1. Martin (Post author)

      Thanks Thorsten πŸ™‚

      Reply
  2. John Stelman

    This is great but got stuck on error when testing from UTM. I have timeout set to 15 seconds, and tried 30 seconds too. Google hasn’t been much help – “failed to recv packet from radius server: timed out waiting for packet” – any pointers appreciated. thx!

    Reply
    1. Martin (Post author)

      Hi, thanks for your reply πŸ™‚
      As the errer states, the RADIUS server does not respond, so check:
      1) Firewall rules on the radius server
      2) Have you setup the correct radius secret and corret UTM IP on the radius server? πŸ™‚

      Reply
      1. John Stelman

        Yes, I have everything set but get this in Event Viewer->Security Events:
        Network Policy Server discarded the request for a user.

        Contact the Network Policy Server administrator for more information.

        User:
        Security ID: AD\testaccount
        Account Name: testaccount@{mydomain}.com
        Account Domain: AD
        Fully Qualified Account Name: ad.{mydomain}.com/{myAD}/Users/Test Account

        Client Machine:
        Security ID: NULL SID
        Account Name: –
        Fully Qualified Account Name: –
        Called Station Identifier: –
        Calling Station Identifier: –

        NAS:
        NAS IPv4 Address: –
        NAS IPv6 Address: –
        NAS Identifier: ssl
        NAS Port-Type: –
        NAS Port: –

        RADIUS Client:
        Client Friendly Name: Sophos UTM
        Client IP Address: 10.0.0.1

        Authentication Details:
        Connection Request Policy Name: Use Windows authentication for all users
        Network Policy Name: Sophos UTM Network Policy
        Authentication Provider: Windows
        Authentication Server: OS-DC-01.ad.{mydomain}.com
        Authentication Type: PAP
        EAP Type: –
        Account Session Identifier: –
        Reason Code: 9
        Reason: The request was discarded by a third-party extension DLL file.

        Reply
  3. John Stelman

    After posting I noticed the connection policy being used. I have two policies. I disabled the ‘use windows authentication for all users’ policy and now the event log just has a blank value instead of my enabled’Sophos UTM Policy’. and the Reason code has changed to 21 with “An NPS extension dynamic link library (DLL) that is installed on the NPS server rejected the connection request.”

    Reply
  4. John Stelman

    I figured this out. I had to add users to the Azure Multi-Factor Authentication app in Azure AD Enterprise apps. It had no members by default.

    Reply
    1. Martin (Post author)

      Hi John,
      Great debugging skills, thanks for sharing πŸ™‚

      Reply
  5. Tobi

    Hi Martin,
    thanks for this how-to. great work.
    one question though:
    i see that this is working with the MFA app confirmation, but is it also possible to use the generated 6-digit code of the authenticator app?
    just in case you might not have internet access with your smartphone or not every use has setup the confirmation via the app turned on.

    Thank you!

    Reply
    1. Martin (Post author)

      Hi, No unfortunately, as the NPS extension works as shown at the top πŸ™‚

      Reply

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