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Zabbix Summit 2022 in Riga: Keeping hundreds of Windows Zabbix agents in sync across different customers

I’m happy to announce that I’ll be one of the speakers at Zabbix Summit 2022 in Riga. As moderator of the Zabbix Telegram and Zabbix reddit community, I was asked by Zabbix to present at the premier event about Zabbix monitoring.

The 10th Zabbix Summit is taking place in Riga, Latvia on October 7-8. My speech is titled:

Keeping hundreds of Windows Zabbix agents in sync across different customers

As a Managed Services Provider (MSP) we are responsible for dozens of customers, with hundreds of Windows Servers. Therefore, we introduced mechanisms to automatically deploy, configure, and sync Windows Zabbix agents across all these isolated environments. In this process, we leverage a tool set consisting of Azure DevOps, Git, PowerShell, and a publicly available Zabbix agent auto-updater, to provide all our customers’ servers with the latest Zabbix agent configuration possible.

Marco Hofmann is an IT-Systems Engineer with 15+ years worth of experience. He works at the german Managed Services Provider ANAXCO GmbH. His priority is the configuration and maintenance of the company’s central Zabbix environment, which is a key component in the fulfillment of the customers’ maintenance contracts. He also focuses on designing and configuring Citrix RDSH environments, fully automated with PowerShell.

Zabbix Telegram Community: https://t.me/ZabbixTech

Zabbix reddit Community: https://www.reddit.com/r/zabbix/

Zabbix website: http://www.zabbix.com/

All speeches from Zabbix Summit will be recorded and uploaded a few weeks later.

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!

Adding Client Printer Redirection for Citrix Workspace App for Mac and Linux to your Citrix Master Image

Today I learned: Citrix Printer Redirection for Mac and Linux is not available Out-Of-The-Box on the Citrix Master Images I install. In this blog post, I will detail the steps I’ve taken to add this missing piece to all of my Master Images.

Introduction

Although quite rare in Germany, a few of our customers use MacBooks at home for the home office. Last week a customer created a ticket, that he couldn’t print on his home printer, although printer redirection was allowed for him in Citrix Studio. At first, I suggested the usual troubleshooting steps, like updating the Citrix Workspace app for Mac and checking the local preferences of the app. Obviously, both didn’t help. I then checked the problem myself and didn’t find an obvious problem. A quick search then led me to two Citrix KB articles, which revealed a knowledge gap on my side:

Client Printing from Linux/MAC is not available on Windows Server 2016 and 2019 (out of the box)

The following Citrix knowledge base articles explain what’s necessary to activate that feature:

  1. CTX283355: Client Printing from Linux/MAC is not working on Windows Server 2016 and 2019
  2. CTX140208: Citrix Workspace App for Mac and Linux fail to Redirect Local printer to Citrix Sessions

Summary of the knowledge base articles:

  1. Download the HP driver update for HP Color LaserJet 2800 Series PS driver from Microsoft Update Catalog.
  2. Inject the driver into the operating system.
  3. Add the printer driver to the printer driver store.
  4. The next time the user logs on, it will just work.

Continue reading “Adding Client Printer Redirection for Citrix Workspace App for Mac and Linux to your Citrix Master Image”

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”

Update Citrix Workspace Environment Management (WEM) to 2106 (2106.1.0.1)

An update guide for Citrix Workspace Environment Management (WEM) to the latest version 2106.

On June 16, 2021 Citrix released version 2106 of Workspace Environment Management (WEM). This is an update guide.
Customer Success Services / Software Maintenance eligibility date: May 15, 2021

Download Citrix WEM 2106 (2106.1.0.1) here:
https://www.citrix.com/de-de/downloads/citrix-virtual-apps-and-desktops/components/workspace-environment-management-2106.html

What’s new:
https://docs.citrix.com/en-us/workspace-environment-management/current-release/whats-new.html

Fixed issues:
https://docs.citrix.com/en-us/workspace-environment-management/current-release/fixed-issues.html

WEM setup files
WEM setup files

Continue reading “Update Citrix Workspace Environment Management (WEM) to 2106 (2106.1.0.1)”