Add a GDPR Footer to the NetScaler Login Page

One of the latest requests I got was to add a GDPR Footer to our NetScaler Login Pages. The Requirement was to display a Link to our Imprint and to our Privacy Policy on the bottom of the Login Page to comply(?) with the new GDRP Requirements.

This can also be used to display other Links or Information. You could for example put a Link to your Helpdesk Portal or to a Self Service Password Reset Site on there.

Implementation:

We start by creating a new Rewrite Action. I decided to name mine rw_act_then_insert_gdpr_footer

Next Step is to configure the needed Expression and Settings for the Rewrite Action. Make sure to edit the HTML Code incuded in the Expression with your needed URLs and Descriptions to your Imprint and/or Privacy Policy (in case of our example).

NetScaler Rewrite Action in the NetScaler GUI

  • Name: rw_act_then_insert_gdpr_footer
     
  • Type: INSERT_BEFORE_ALL
     
  • Expression to choose Target Location: HTTP.RES.BODY(120000).SET_TEXT_MODE(IGNORECASE)
     
  • Expression: "var login_footer=$(\"<br><div style='text-align:center;color:white;font-size:15px;'><a target='_blank' style='color:white;text-decoration:underline' href='https://www.example.com/imprint'>Imprint</a>"+"  |  "+"<a target='_blank' style='color:white;text-decoration:underline' href='https://www.example.com/privacy'>Privacy Policy</a><br></div>\").appendTo(logonbox_container);"
     
  • Pattern: box_view.prepare_view()

When done this should look something like this:

Completed Rewrite Action in the NetScaler GUI

Now it's time to configure the Rewrite Policy. According to my Naming Scheme I've choosen to go with rw_pol_then_insert_gdpr_footer

  • Name: rw_pol_then_insert_gdpr_footer
     
  • Action: rw_act_then_insert_gdpr_footer
     
  • Expression: HTTP.REQ.URL.CONTAINS("gateway_login_view.js")

The final Rewrite Policy should look like this:

Last Step is to bind the newly created Footer to the NetScaler Gateway vServer where we want to display the Links. In my case I have a lot of rewrite Policies so make sure you set your GoTo Expression to Next. This is how my Rewrite Policy Bindings on the NetScaler Gateway vServer looks like.

And this is the Result when done correctly

Note:

This Rewrite Policy only works with the Classic, Greenbubble and X1 Theme. The newer RfWebUI Theme is not supported.

Code:

If you don't want to use the GUI you can also use the following NetScaler CLI Commands to create the required Rewrite Policy and Rewrite Action.

add rewrite action rw_act_then_insert_gdpr_footer insert_before_all "HTTP.RES.BODY(120000).SET_TEXT_MODE(IGNORECASE)" q{"var login_footer=$(\"<br><div style='text-align:center;color:white;font-size:15px;'><a target='_blank' style='color:white;text-decoration:underline' href='https://www.example.com/imprint'>Imprint</a>"+"  |  "+"<a target='_blank' style='color:white;text-decoration:underline' href='https://www.example.com/privacy'>Privacy Policy</a><br></div>\").appendTo(logonbox_container);"} -pattern "box_view.prepare_view();"

add rewrite policy rw_pol_then_insert_gdpr_footer "HTTP.REQ.URL.CONTAINS(\"gateway_login_view.js\")" rw_act_then_insert_gdpr_footer

NetScaler Ciphers and the ROBOT Attack

Here we are again with another Vulnerability related to the SSL/TLS Ecosystem called the ROBOT Attack (robotattack.org) and that usually means the NetScaler is also affected or you need to change some part of your SSL/TLS Configuration.

Besides updating your NetScaler Firmware to one of the latest Builds (see CTX230238 for fixed Builds) you need to remove all Ciphers starting with TLS_RSA from your Cipher List. Below is a Cipher List where all the Ciphers with RSA Encryption are removed to prevent the ROBOT Attack.

You could alternatively also use the Modern Compatibility Cipher List:

https://docs.citrix.com/en-us/receiver/windows/4-7/configure/ica-import-icaclient-template-v2.html

Important Note: Only Citrix Receivers for Windows starting with Version 4.7 or higher can connect to your published Desktops/Applications after applying the new Cipher List. This is because ECDHE Cipher Support was first implemented with Receiver 4.7 and we have removed all the other supported Ciphers starting with TLS_RSA_*.

You can see a List of supported Ciphers for the Citrix Receiver starting with Version 4.7 below: 

https://docs.citrix.com/en-us/receiver/ios/7/secure-communications.html

Update #1: I had to learn the hard way that the Citrix iOS Receiver 7.4 can't work with the posted Cipher Lists because the iOS Receiver only supports Ciphers starting with TLS_RSA_*.

Hopefully Citrix will soon release a new Version with additional Cipher Support.

Update #2: The Problem with the Citrix iOS Receiver has been fixed in the 7.5 Version. You can now use the new Cipher List with the latest iOS and Android Receivers.

Verification:

As always test your updated Configuration with the SSLLabs Test or use the Comodo SSL Analyzer.

Feedback and Comments is as always very welcome.

NetScaler Cipher Lists - 2016 Edition with ECC/ECDSA

The new NetScaler 11.1 Release (starting with Build 47.14) brings Support for ECC/ECDSA Ciphers, unfortunately only on MPX Appliances with a N3 SSL Accelerator Chip for now.

Next on my Wish List would be ECC/ECDSA Support on VPX/CPX, OCSP Stapling and ChaCha20-Poly1305 Support.

The new updated Cipher Lists are grouped into a Modern and a Intermediate Cipher List Group based on the Recommendations from the Mozilla Wiki. If you want to use the Intermediate Cipher List don't forget to create a 2048bit DH Parameter and bind it to your vServer (or your SSL Profile).

  • Mozilla Modern:
Oldest Supported Clients: Firefox 27, Chrome 30, IE 11 on Windows 7, Edge, Opera 17, Safari 9, Android 5.0, Java 8
TLS Versions: TLS1.2 only

  • Mozilla Intermediate:
Oldest Supported Clients: Firefox 1, Chrome 1, IE 7, Opera 5, Safari 1, Windows XP IE8, Android 2.3, Java 7
TLS Versions: TLS1.0, TLS1.1 TLS1.2


After the Break are the Cipher Lists from my older Blogposts for Reference if you are running an older Version:



Cipher List for MPX/SDX and VPX (starting with Build 11.0-65.31) Appliances:

Legacy Cipher List for MPX/SDX and VPX (starting with Build 11.0-65.31) Appliances:

Cipher List for VPX starting from Build 10.5-57.7 up to 11.0-64.34:

Legacy Cipher List for VPX Builds starting from Build 10.5-57.7 up to 11.0-64.34:

Public Key Pinning (HPKP) with NetScaler

I recently decided to implement HTTP Public Key Pinning (HPKP) for some of our external facing Services and our NetScaler Gateway/Access Gateway.

Before we go on I recommend reading through the Wikipedia Article and this Blogpost from Tim Taubert to get a basic understanding of how HPKP works. Tim can also explain it a lot better than I can.

In this Guide I'm assuming you already have some kind of Load balancing vServer or NetScaler Gateway set up and running (including an existing SSL Certificate). So let's start:

In my Example I choose to pin the used Certificate itself and the Intermediate Certificate from RapidSSL where the Certificate itself was issued from. Please make sure you know the consequences when choosing the Certificate Hashes you are going to pin.

First off we need to generate the SHA256 Hashes for the Certificates we want to "pin". I choose to do it via the OpenSSL Interface in the NetScaler GUI but you could also choose to do the same via the NetScaler Shell CLI.

Just copy and paste the following Command into the Command Window and let OpenSSL do its magic. Copy or write down the created Hash as we will need it later on.

x509 -in /nsconfig/ssl/name-of-your-servercertificate.cer -pubkey -noout | openssl rsa -pubin -outform der | openssl dgst -sha256 -binary | openssl enc -base64

Rinse and repeat for the second Certificate (the Backup Hash) you want to pin. In my case this is the issuing Intermediate Certificate from RapidSSL.

x509 -in /nsconfig/ssl/name-of-your-intermediate.cer -pubkey -noout | openssl rsa -pubin -outform der | openssl dgst -sha256 -binary | openssl enc -base64

Next up we need to create the Rewrite Action and the Rewrite Policy to insert the needed HPKP HTTP Header into the HTTP Responses for our vServers and/or NetScaler Gateways.

First lets create a Rewrite Action. I named mine "insert_HPKP_header":

Name: insert_HPKP_header
Type: INSERT_HTTP_HEADER
Header Name: Public-Key-Pins
Expression: "pin-sha256=\"yourcerthashgoeshere\"; pin-sha256=\"yourbackuphashgoeshere\"; max-age=60; includeSubDomains"

Important: For the max-age I recommend starting with a low Value like 60 seconds during the Implementation Phase because if you somehow fuck up your Hashes you are only locked out for 60 Seconds. After successfully testing your HPKP Headers you should then ramp it up to something like 5184000 seconds.

Next Step is to create the needed Rewrite Policy itself. Mine is called enforce_HPKP and is just using TRUE as Expression.

Now its time to bind the newly created Rewrite Policy onto the vServer and/or the NetScaler Gateway Server. If you have multiple Rewrite Actions with different Priorities bound to the vServer (like in my case) make sure to set the "Goto Expression" Option to NEXT or otherwise only the first Rewrite Action will be applied. 

Last but not least you should check if the Public-Key-Pins Header is added successfully to your HTTP Responses. An easy Way is using the SSLLabs.com Scanner and check the Public Key Pinning Test. If everything is working you can now ramp up the max-age Value to 5184000.

If you don't like the NetScaler GUI you can also use the following CLI Commands to implement it:

add rewrite action insert_HPKP_header insert_http_header Public-Key-Pins q{"pin-sha256=\"yourcerthashgoeshere\"; pin-sha256=\"yourbackuphashgoeshere\"; max-age=60; includeSubDomains"} 
add rewrite policy enforce_HPKP TRUE insert_HPKP_header
bind vpn vserver nameofyourvserver -policy enforce_HPKP -priority 100 -gotoPriorityExpression END -type RESPONSE

Update: Implement HPKP Reporting

HPKP includes a Reporting Functionality for the Clients (Browsers) to send a Report in case of an Error. There is a great and free Service called report-uri.io from Scott Helme you can use to avoid having to set up your own Report Server.

After registering at report-uri.io you are given a unique Report URL you have to add to the HTTP HPKP Header as an additional Parameter. In this Example we would use the Public-Key-Pins-Report-Only Header (instead of the Public-Key-Pins Header) without enforcing HPKP itself. This would be a good first Step to see if your calculated Certificate Hashes in the Header are correct without blocking your Site in case of a wrong Hash.

Name: insert_HPKP_header_reportonly
Type: INSERT_HTTP_HEADER
Header Name: Public-Key-Pins-Report-Only
Expression: "pin-sha256=\"yourcerthashgoeshere\"; pin-sha256=\"yourbackuphashgoeshere\"; max-age=60; includeSubDomains; report-uri=\"https://report-uri.io/report/667d4f42bdc27b357863fefdd41574a4\""

The CLI Command for creating the would be

add rewrite action insert_HPKP_header_reportonly insert_http_header Public-Key-Pins-Report-Only q{"pin-sha256=\"yourcerthashgoeshere\"; pin-sha256=\"yourbackuphashgoeshere\"; max-age=2592000; includeSubDomains; report-uri=\"https://report-uri.io/report/667d4f42bdc27b357863fefdd41574a4\""}
add rewrite policy enable_HPKP_Reporting TRUE insert_HPKP_header_reportonly
bind vpn vserver nameofyourvserver -policy enable_HPKP_Reporting -priority 100 -gotoPriorityExpression END -type RESPONSE 

 As always Feedback and Comments are greatly appreciated.

Perfect Forward Secrecy and NetScaler MPX Revisited

My last Blogpost regarding Perfect Forward Secrecy on NetScaler got a lot of Comments and in the meantime Citrix released a new NetScaler Firmware Versions (10.5-53.9.nc) which now enables us to use ECDHE Ciphers even on "low end" NetScaler MPX Models like the MPX 5500.

With the new Firmware it's now possible to enable PFS for all modern Clients/Browser and receive an A+ in the SSLLabs Test.

Okay, let's start:

First step is to create a new Cipher Group where we will bind all the new Ciphers we want and need.

Unfortunately changing the Order via the NetScaler GUI is not very user-friendly (Hey Citrix, please enable us to easily change the Cipher Order) so I resorted to the Command Line. Below are the commands to create a new Cipher Group called "THEN-High" and bind the Ciphers in a preferred Order (I'm open for Discussions on the Order and Ciphers if you disagree or got a better Order):

Important: Make sure to order the Ciphers in the preferred order (thanks again to David Chivers for pointing this out) or you may not get Forward Secrecy to work on some Clients/Browser.

Cipher List for MPX/SDX and VPX (starting with Build 11.0-65.31) Appliances:

Legacy Cipher List for MPX/SDX and VPX (starting with Build 11.0-65.31) Appliances (includes Support for WinXP, Java and Android 2.x):

Cipher List for VPX starting with Build 10.5-57.7 up to 11.0-64.34:

Legacy Cipher List for VPX Builds starting with Build 10.5-57.7 up to 11.0-64.34 (includes Support for WinXP, Java and Android 2.x):

Since NetScaler 11 Citrix now seems to enforce compatible Ciphers on the VPX Platform.

All SHA2 and GCM Cipher Suites are not (yet?) supported on the VPX. Since NetScaler Build 11.0-65.31 the VPX now supports all AES-GCM/SHA2 Ciphers. Hooray!

And thats what it looks like in the GUI:

Don't forget to create a Diffie Hellmann Key (2048bit Keysize recommended) and configure it under the SSL Parameters on the vServer (or use the new SSL Profiles Feature). You can find a detailed How-To in my old Blogpost here.

The next Step is to bind the newly created Cipher Group to the vServer. When I did this via the GUI my Cipher Order wasn't honored (Bug? Anyone else?) so again I needed to use the Command Line:

bind ssl vserver <vServerName> -cipherName THEN-High

(Update: With the 10.5-57.7 NetScaler Build this Bug has been fixed by Citrix! You can now use the GUI to bind the Cipher Group.)

Don't forget to bind ECC Curves on the vServer or you won't be able to use the newer ECDHE Ciphers. I recommend binding the Curves P_256, P_384 and P_521.

bind ssl vserver <vServerName> -eccCurveName P_256 P_384 P_521

Let's take a look in the GUI (note the correct Cipher Order):

After configuring everything correctly you should check it using the SSLLabs Test. Here is my Result with the latest Firmware and the described Settings:

(Update: With the 10.5-57.7 NetScaler Build you can now get the A+ Rating in the SSLLabs Test because Citrix added TLS_FALLBACK_SCSV Support)

As always feel free to leave a Comment.

Changelog:

#1 - 19.05.2015 - Cipher Reordering Bug has been fixed by Citrix with the 10.5-57.7 NetScaler Build
#2 - 19.05.2015 - Note regarding TLS_FALLBACK_SCSV Support in the 10.5-57.7 NetScaler Build
#3 - 22.05.2015 - Added specific Cipher List for NetScaler VPX with the 10.5-57.7 NetScaler Build
#4 - 21.06.2015 - Added Note regarding binding ECC Curves.
#5 - 30.06.2015 - Updated MPX/SDX Cipher List with some new Ciphers for broader Client Support.
#6 - 01.07.2015 - Changed VPX Cipher Suite for NetScaler 11 regarding the support of SHA2 and GCM Cipher Suites
#7 - 10.09.2015 - Added MPX/SDX Cipher List without DHE Ciphers (Logjam)
#8 - 02.03.2016 - Added 2 new Ciphers for the VPX Platform Cipher Group
#9 - 04.03.2016 - moved Code to GitHub Gists for Versioning and Change Tracking
#10 - 22.03.2016 - Since NetScaler 11.0-65.31 the VPX now supports all AES-GCM/SHA2 Ciphers. Hooray!