Author: Jørgen Rosenkvist Pedersen Page 3 of 5

NetScaler, you are in control

On June 8, 2018

As a consultant I often debug on NetScaler related issues. When I do this debugging I use different methods like nstcpdump, nstrace.

Nstcpdump I normally use just to clarify where we are sending data and if we are getting any response – this can tell if there are routing or Firewall issues.

SNIP = 10.11.12.152, Web Server = 192.168.1.152 port 8443

Routing problem, only sending data no answers:

Firewall Block, only sending data no answers:

And when it works we see monitoring data every 5 sec. (default):

As you see we can not tell from the nstcpdump if it is a routing problem or a Firewall block. We can only see that we are sending monitor data but never get any answer back.

The above is just for quick debugging on network related issues. When we want to do some deeper debugging nstrace is the tool to use.

As I do this it is important to inform the customer that we can see everything, and I mean EVERYTHING. I think this is important because we can see data that was not intended for us to see.

Let me show you.

I just do a simple nstrace with this command:

start nstrace -size 0

and stop it again with this command:

stop nstrace

The trace file will be in the /var/nstrace catalog on the NetScaler. Opening the trace that I just made looks like this (filtered with “frame contains “nsroot””:

As the trace show I just did a logon to my NetScaler while the trace was running, and I can se what username and password was provided. No surprise, I use the default nsroot, nsroot for my test NetScaler which is not in production.

But what if a user at the same time did a logon to the VIP = 10.11.12.156 for the Web Server 192.168.1.152?

Yes, I can see that too:

But what if we are using SSL connections? Well that is not a problem as we can get the NetScaler to decrypt the trace by doing this command (Not on SSL_BRIGDE sessions):

start nstrace -size 0 -mode SSLPLAIN

With that the login for an SSL session will be in clear text within the trace. I have not made screenshots of that as It will look just like the above screenshots.

But what do we then do to keep our back safe. Well we can do some filters on the traces, so we only see the traffic we are interested in.

Here are some examples.

To see traffic to and from a specified host:

start nstrace -size 0 -filter CONNECTION.DSTIP.EQ(192.168.1.152).OR(CONNECTION.SRCIP.EQ(192.168.1.152))

To see traffic for a specified port:

start nstrace -size 0 -filter CONNECTION.PORT.EQ(514)

By using filters on that nstrace command we only get the traffic we need for debugging on a specified system.

And again, remember to get permission to do the trace and tell the customer that when we do this we can see all traffic to and from a system.

Conclusion:

Well, this is only best practice for us NetScaler consultanst. We need to inform the owner of the system that when we do debugging on their system, we can get data that was not intended for us to see. Always keep a good and open dialog with the system owners so that we don’t get into trouble.

NetScaler CLI, Watch Out

By Jørgen Rosenkvist Pedersen

On April 11, 2018

In Uncategorized

A lot of my NetScaler configurations are done at NetScaler Command Line Interface (CLI). Bye doing this I am sure that I remember to set all the parameters of a service or other stuff.

But do you know about the “history” command?

This will display the lasted command used in NetScaler CLI. Here is an example:

Be aware that when you use CLI, that you never type password in the CLI command as other users can see this.

Here I created a local NetScaler user at CLI, and this is what are displayed in that history:

A better way is to use the -password when creating or changing password for a user. Like this:

When using the -password option, this is what is displayed in the history:

I think that Citrix is wrong when writing the CLI commands in some of their articles, like this one:

https://support.citrix.com/article/CTX224027

The god thing is that the history is pr. user list. With the nsread user I can’t see the CLI commands done by the nsroot:

Unforcedly it is not possible to clear the history list in NetScaler kernel mode, as discussed here:

https://discussions.citrix.com/topic/386456-clearing-cli-history-security-concerns/

My college Allan has blogged about history issue with PowerShell, see his blog here:

https://www.virtual-allan.com/powershell-command-history/

Conclution

Well the NetScaler CLI is powerful and is god to use. Another benefit of using the NetScaler CLI is that you will soon be abled to read the full NetScaler configuration file (ns.conf)

As I wrote in this blog just be aware of the history and avoided using password in CLI commands.

Maybe Citrix will consider making a command to clear the history list.

Citrix NetScaler, Custom logging

By Jørgen Rosenkvist Pedersen

On March 27, 2018

In Uncategorized

We, my college and I, where doing a XenMobile installation at a customer, which had a strict logging policy. The users where allow internet access through Secure Web App in XenMobile.

All internet traffic had to go out of the company Firewall, for security reasons. When doing this the NetScaler SNIP is logged in the Firewall, but the customer wants the user’s devices IP address logged.

We came up with a custom logging solution with a syslog server. The syslog server configuration on the NetScaler was done, se more here:

How to Configure Syslog on a NetScaler Appliance

https://support.citrix.com/article/CTX121728

When that was done, I configured an Auditing Message Actions:

With this I log the device IP and the requested URL.

The I made an Rewrite policy, with the flowing settings:

This will not do any rewrite, as action is set to NOREWRITE, but it will use the Auditing Message Actions and send the information to the syslog server.

Finally, I bound the rewrite policy to the XenMobile Access Gateway configuration:

For the test I tried to access http://dr.dk with in the Secure Web App, and I found the flowing logging on the syslog server:

Conclusion:

We ended up with a logging of the device IP and the access URL. With the many expressions available on the NetScaler you would be able to log almost everything in the syslog server.

Remember to bound the rewrite policy with NEXT as Goto Expression, or you could end up with others rewrite policies not being processed.

CLI commands:

add audit messageaction log_act_custom ALERT “\”Client:\”+CLIENT.IP.SRC+\” accessed \”+HTTP.REQ.URL”

add rewrite policy log_rw_pol true NOREWRITE -logAction log_act_custom

bind vpn vserver < Gateway virtual server name> -policy log_rw_pol -priority 100 -gotoPriorityExpression NEXT -type REQUEST

NetScaler GEO IP Web Site Protection

By Jørgen Rosenkvist Pedersen

On January 16, 2018

In Uncategorized

You can use the NetScaler to make GEO IP filter to your Web Sites. This can enhanced your security, as traffic only from specified countries is allowed. You can have Web Sites with data you don’t wont specified countries to access.

You can also use it to send users from specified locations to specified Web Sites, with are customized for them.

In the flowing example I simply block all traffic not from DK locations.

First check if your GEO IP is imported:

Update:

In the new build of Citrix ADC/NetScaler the GEO IP Database is included. You only need to enable the Citrix ADC/NetScaler to you it:

add locationFile /var/netscaler/inbuilt_db/Citrix_Netscaler_InBuilt_GeoIP_DB_IPv4

set locationParameter -matchWildcardtoany YES

***** Old blog, start *****

If status is “Not Loaded” upload the GEO IP Database to /var/geoip

I have downloaded the GEO IP Database from http://geolite.maxmind.com/download/geoip/database/GeoIPCountryCSV.zip

Unforcedly this is a legacy database and maintains of this will stop, but for testing the configuration it will be fine. This is the statement from MAXMIND:

After uploading the file “GeoIPCountryWhois.csv” to the /var/geoip/ you need to configure the NetScaler to load it:

Control that it is loaded:

As after NetScaler Version 11.1 Build 53.11 you need to enable wildcard search, with this:

***** Old Blog, end *****

For testing, I have made a response action:

And a response policy:

Now bind the responder policy to the Load Balancing vServer, and test.

To trigger a block a simply change the DK to another country, as I have no way to test from other than DK IP addresses. When changing to SE, I get the flowing message when testing:

I recommend that you simply use a drop, to hide that you actually make the GEO IP check. You can do that with:

Conclution:

GEO IP can be used to enhanced your security as you can set a policy to witch country that are allowed to access a Web Site or a Access Gateway.

You can use GEO IP to send users to specified Web Server based on their public IP Adresses.

CLI Commands:

show locationparameter

add locationfile /var/geoip/GeoIPCountryWhois.csv -format GeoIP-Country

set locationParameter -matchWildcardtoany YES

add responder action res_act_display_blocked_page respondwith “\”Sorry, the IP address you are connecting from (\”+CLIENT.IP.SRC+\”) is detected as untrusted. Access to our systems from your location is not allowed.\””

add responder policy res_pol_drop_non_dk “CLIENT.IP.SRC.MATCHES_LOCATION(\”*.DK.*.*.*.*\”).NOT” res_act_display_blocked_page

set responder policy res_pol_drop_non_dk -action DROP

Citrix Receiver Auto-update

By Jørgen Rosenkvist Pedersen

On January 10, 2018

In Uncategorized

With the new Citrix Receiver Auto-update function, it is important to select the right update program that fit your installation.

You may not want users to update their Citrix Receiver them self, as your helpdesk has to deal with different versions of the Citrix Receiver. If your organization requires that you be in the LTSR program, then you have to set this on the installation/policy.

If using installation parameters the flowing can be used:

To test I have run this installation:

This end up with these registry settings:

Be aware that I have run the installation as an administrator. If you run the installation as a user then the settings will be under HKEY_CURRENT_USER and not under HKEY_LOCAL_MACHINE.

You can allow control the update feature with policies:

Conclution:

My point is that it is important to think of the update feature, when deploying Citrix Receiver. I have seen customers that did not control this and end up with many calls to the helpdesk, because Citrix Receiver started to update on the clients. A lot of cleanup had to be done because clients had different versions of the Citrix Receiver installed.