Citrix NetScaler Gateway: NPS Extension for Azure MFA fails after introducing the Microsoft Domain Controller security baseline

Microsoft offers a nice set of security baseline GPOs, for direct use in your Active Directory environment. If you make use of the “MSFT Windows Server 2022 – Domain Controller” policy, your NPS installation might start to fail.

Introduction

Many of you probably have a Citrix NetScaler Gateway installation based on the following concept:

Manuel Winkel (deyda):

Microsoft Azure MFA Cloud Service in Citrix ADC

Thomas Preischl:

Citrix ADC / Netscaler Azure MFA Authentication

Those articles describe, how someone can implement Azure MFA with Microsoft Authenticator App pushOTP and an on-premises Microsoft NPS server, without making use of SAML, which is necessary, if you use the ICAProxy Gateway only license for Citrix NetScaler Gateway.

The Error

While implementing the Microsoft security baselines at a customers’ site, we also introduced the Domain Controllers security baseline called:
MSFT Windows Server 2022 – Domain Controller

MSFT Windows Server 2022 - Domain Controller
MSFT Windows Server 2022 – Domain Controller

A few minutes later, the external Citrix NetScaler Gateway authentication stopped working. Users would only receive the error:
Unknown username or password

Citrix NetScaler Gateway - Login failed
Citrix NetScaler Gateway – Login failed

Troubleshooting on the Citrix NetScaler Gateway through the aaad.debug showed the following error:

MS-CHAP error ERROR_AUTHENTICATION_FAILURE (691)

MS-CHAP error ERROR_AUTHENTICATION_FAILURE (691)
MS-CHAP error ERROR_AUTHENTICATION_FAILURE (691)

While the event viewer on the NPS server told us:

NPS Extension for Azure MFA: NPS Extension for Azure MFA only performs Secondary Auth for Radius requests in AccessAccept State. Request received for User Marco.Hofmann with response state AccessReject, ignoring request.

NPS Extension for Azure MFA only performs Secondary Auth for Radius requests in AccessAccept State. Request received for User Marco.Hofmann with response state AccessReject, ignoring request.
NPS Extension for Azure MFA only performs Secondary Auth for Radius requests in AccessAccept State. Request received for User Marco.Hofmann with response state AccessReject, ignoring request.

The solution

The error weren’t helpful at all. We spent quite too much time searching for an indicator of what might be the issue. We knew it must have to do with the Domain Controller security baseline. Finally, we stumbled at the following post from serverfault.com:

https://serverfault.com/questions/608227/authentication-via-radius-mschapv2-error-691

One of my colleagues was at a Microsoft conference having various discussions when it dawned on him that MSCHAPv2 relies on NTLM to generate the password challenges and responses. Now plain old MSCHAP and MSCHAPv2 (i.e. not EAP-MSCHAPv2 or PEAP) when used in Windows RAS services will use NTLMv1 by default.

As many of of you have already started to catch on, we, like many administrators, have disabled NTLMv1 on our DCs and as such the DCs will only accept NTLMv2 requests. This explains why the failure I continued to get was a “bad password” error. The password being sent to the DCs was in NTLMv1 format and was getting ignored.

This post then lets to a Microsoft article, with the solution:

https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/rras-vpn-connections-fail-ms-chapv2-authentication

For example, when you set this value to 5 (Send NTLMv2 response only. Refuse LM & NTLM), the DC won’t accept any requests that use NTLM authentication. When MS-CHAP or MS-CHAPv2 are configured, RAS in Windows Server 2008 R2 will default to NTLM to hash the password. Because the DC only accepts NTLMv2, the request will be denied.

Microsoft NPS on Windows Server 2019 and 2022 will use NTLMv1 by default, if you make use of MS-CHAPv2. And the MSFT Windows Server 2022 – Domain Controller security baseline will turn off NTLMv1 for your Domain Controllers, which will break your NPS server.

To enable NTLMv2 for MS-CHAPv2, you must set the following registry key on your NPS server, and restart the NPS service, and it will start working again:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RemoteAccess\Policy]
"Enable NTLMv2 Compatibility"=dword:00000001

Enable NTLMv2 Compatibility
Enable NTLMv2 Compatibility

I hope this will help someone else!

Transition from BIS-F version 6.1.3 to 7.1912.x

With the release of the Base Image Script Framework (BIS-F) version 7.1912.x a few minor changes in the ADMX template files occurred.

We are going to outline the changes necessary to your current deployment.

Continue reading “Transition from BIS-F version 6.1.3 to 7.1912.x”

Caution: FSLogix 2009 (2.9.7621.30127) profiles won’t logoff completely

At three customer sites I created test machine catalogs with FSLogix 2009, and all of them had the same issue, that FSLogix profiles won’t logoff completely at the end of the day.

Update January 11, 2021: I was informed about a better solution via Twitter, and updated the Blog post accordingly.

The Problem

During my personal tests with FSLogix 2009 (2.9.7621.30127) I discovered that the profiles won’t logoff completely at the end of the day. See the following screenshots.

You can clearly see, that despite there are no active or disconnected user sessions, some of the VHDX disks are still mounted, but more important the folders from C:\users\ won’t vanish.

This makes a second login impossible on the same VDA.

Download and install latest Office 365 via Office Deployment Tool (ODT)

Inspired by Trond Eric Haavarstein’s evergreen PowerShell setup scripts, I created a download and install script for Office 365 Deployment Tool (ODT).

Microsoft Office 365 is the new standard in the EUC space right now. To honor this, we need a fast and reliable way to install it with our favorite deployment tools like MDT or PDQ,  for example when you rebuild your master images.

There are a few different ways to deploy Office 365, but they are all similar:

  • You need the Office 365 Click-to-run setup.exe (Office Deployment Tool (ODT))
  • You need a XML configuration file
  • You decide to deploy from a pre-build offline cache or the files are downloaded from Microsoft each and every time

And then you go: setup.exe /configure configuration.xml

Pretty straight forward you think, but non the less I had problems with this approach. And this is due to the fact, that the Office Deployment Tool itself gets updated pretty often. And this breaks your unattended deployments sooner or later, as the setup.exe stops working. Continue reading “Download and install latest Office 365 via Office Deployment Tool (ODT)”

Release of FSLogix Apps release 2004 (2.9.7349.30108)

Today Microsoft released FSlogix Apps release 2004 (2.9.7349.30108)

You can find the source of the announcement here, including the Release Notes. A copy of the original release notes are quoted below.

Source: https://social.msdn.microsoft.com/Forums/en-US/e82cb114-2459-4a99-bcbf-50b7d314b5b9/release-notes-for-fslogix-apps-release-2004-29734930108?forum=FSLogix

Release Notes: Continue reading “Release of FSLogix Apps release 2004 (2.9.7349.30108)”