One of the main concerns that my large customers have is that the Citrix Gateway could fall victim to a DOS or DDOS attack. Linked to this, of course, is the concern that – after a successful attack – it might be possible to bypass authentication or compromise the gateway or the appliance. We have to distinguish between attacks that happen before and those that happen after...
last updated: April 26 2022 I am currently creating a slide deck for a CUGC event on May 11. It will be about securing Citrix (NetScaler) Gateway. During my work, I wanted to find out, what the cookie NSC_VPNERR is good for. After a successful login, its value is set to 3 (Citrix ADC 13.0, it’s not documented). With most of the current browsers, you have to press F12 to see the...
Recently, I had to add a pop-up window to a webpage. It should display every time users from a certain region surfs to this site. In this very case, it’s been information on Putin’s war against Ukraine. My customer’s idea had been to bypassPutin’s ban of information. However, however, did not want to touch each and every page, and it had to be dependent on the country:...
Recently I had a SPAMer here in my blog, who wanted to place his links here. I don’t know why he had chosen this blog, in particular, I also don’t know what he expected from it, because all entries here are moderated. I have always approved all entries, that had been professionally appropriate, but I do not allow SPAM. But, of course, it’s overhead for me. Anyway, no matter why...
last update: July 12th 2022 If someone makes a typing error when entering the domain name, he will not get a valid response. This is a typical example: You can clearly see: The response got an NXDOMAIN status, a non-existing domain. This, however, is not always desired, instead, you might want to return an IP address. It should have looked like this: This time, you see an answer section. The IP...
There is a question coming up every now and then: How to extend space on a Citrix ADC formerly called NetScaler. First of all: There is absolutely no supported way to do so! With this in mind, we can continue. Is there a real need to extend the disk space? The answer is no. There is plenty of space for all needs. You said, there is space enough, why did I run out of diskspace? That’s hard...
Last update: December 22nd 2021 Many of us, today, struggle with the Log4J security issue (CVE-2021-44228). It will take a long time to fix all apps, as the Apache log4J framework is built deep into several apps. For many of my customer’s apps, it’s still not clear, if whether they are affected, or not. At the same time, there are already exploits out there, allowing attackers to get shell access...
last update: February 21st 2022 Recently, I had been asked, how to protect a gateway from threads. It’s easy, I thought, Citrix ADC has everything needed in good quality: A Bot Management, Web Application Firewall (WAF), and AppQoE (Application quality of experience, a DOS protection feature). So nothing easier than that: Create the policies desired and bind them to the gateway. Shortly...
HTTP v3 and HTTP v2 on a Citrix ADC / NetScaler last update: February 28th 2022 HTTP/1.0 and HTTP/1.1 are dead. They are inefficient plain text protocols. The amount of data to be transferred is huge and latency is a big problem, mostly for intercontinental connections. But what alternatives do we have? Are there alternatives? A view on the history of HTTP HTTP/0.9 – The one-line protocol The...
There is something I frequently get asked for: How can we find out, which users use which ciphers? Will Citrix ADC show this information? Does ADM show it? A simple answer would be: No chance, ADC can’t do it at all. ADM – however – can do. If you don’t like ADM (I’d wonder why) you can’t. Let’s not make things that simple. We all are engineers. The word...