Potentially ongoing worldwide UDP:443 (EDT) DDoS amplify attack against Citrix (NetScaler) Gateway

Since 19 December 2020 7pm CET we see a possible worldwide DDOS amplify attack against Citrix Gateway UDP:443 DTLS EDT services.


  • 11.01.2021: Added information about the new Citrix ADC Gateway (formerly NetScaler) firmware releases, which solve the memory leak issue with -helloVerifiyRequest
  • 24.12.2020: Added information about the official Citrix Knowledge Center article CTX289674
    Added a final summary, that repeats all possible solutions
    Maked it a lot clearer, that -helloVerifiyRequest doesn’t seem to work well
  • 22.12.2020: Added a warning note, that -helloVerifiyRequest doesn’t work on all Citrix ADC (NetScaler) firmware versions
  • 21.12.2020: Added a third possible solution regarding -helloVerifiyRequest
  • 21.12.2020: Initial version

The situation

During the night from Saturday (19.12.2020) to Sunday (20.12.2020) our Zabbix Monitoring informed us, that several Citrix Gateway VPX (50) appliances were at its license cap. We investigated the situation and soon found out, that we had 0 ICA sessions on most of them, hence no explanation for the traffic.

Zabbix Citrix Gateway Throughput Monitoring Graph
Zabbix Citrix Gateway Throughput Monitoring Graph

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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)”

Zabbix Frontend Modules

Leveraging the new feature of Zabbix 5.0 LTS, these Frontend Modules can extend the Zabbix Sidebar menu.


You can read more about this new feature in the official Zabbix documentation:

The modules in this repository were tested on Zabbix 5.0.2+ on Debian 10 Buster.

Frontend modules
Frontend modules

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HowTo: Update Seafile Server for generic Linux to version 7.1.5 64bit

Seafile Server is an open source alternative to public cloud storage providers like Dropbox, Microsoft OneDrive, Apple iCloud, Google Drive and Citrix Sharefile. It works on free Linux Distributions like Debian and gives you the freedom to use the comfort of a modern synchronization client, the simplicity of a modern WebGUI, completed with the knowledge where your data is and who can access it.

If you are searching for the update guide for Seafile 6.x to 7.0.x, please find the old article below. Thank you!


  • 01.11.2020: Post updated for Seafile Server 7.1.5
  • 04.05.2020: Post updated for Seafile Server 7.1.3 and archived previous guide below, as it’s still relevant, if you want to upgrade from 6.x to 7.1.x
  • 24.12.2019: Post update for Seafile Server 7.0.5
    Reworked WordPress link structure, to point all update guides to a new static URL.

Since 22.09.2020 the fifth maintenance release version 7.1.5 is public available. Please see the official changelog:

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