3.1.1. Lab 1 - TLS Version Control

3.1.1.1. Scenario

If you care about security at all, then you also need to care about SSL and TLS. These are the protocols that provide encryption to the Internet traffic. It’s the "S" in HTTPS, FTPS, and IMAPS. You get the picture!

Without encryption, all communication between a client and server is visible for any third party to see and this can have some pretty devastating effects. Encryption is a cornerstone of network security. If you’ve been paying attention to the news the last few years, you’re probably also aware that SSL and TLS are not without their own flaws. Exploits like BEAST, Heartbleed, and POODLE take advantage of specific holes in the SSL and TLS protocols. To stay ahead of these vulnerabilities, industry best practices suggest that we avoid some versions of these protocols specifically SSLv2, SSLv3, and now TLSv1. This also applies to certain ciphers such as MD5, RC4, and eventually the RSA key exchange.

The F5 BIG-IP platforms make it extremely easy to control and enforce these protocols and ciphers but at the same time, you may not simply want to "break" some users. If your income depends on Internet commerce, the last thing you may want to do is block customers from buying from you because they have a slightly out-of-date browser. Eventually, most of these older browsers will go away or at least enough of them that you can justify disabling lower encryption protocols and ciphers. But, how do you know?

F5 iRules have access to everything in the OSI layers from 3 to 7 that includes some pretty rich information about SSL and TLS. Let’s take a look at an iRule that will catalog the SSL/TLS versions that clients are using.

Note

A word on "mixed content" – All too often, developers or development platforms provide access to both HTTP and HTTPS content within the same application. This is referred to as "mixed content" and can have some significant security implications. For example, an application may redirect a user to an HTTPS URL to authenticate, but then switch back to HTTP after authentication to access normal application content. At the very least, the HTTPS authentication is very likely going to set up a "session" with the user, which will also very likely to be maintained by an HTTP cookie in the browser. If the application session is now communicating via HTTP, all of that user session information is in the clear. Long story short, don’t allow mixed content in your applications. If there is anything in your application worth protecting with encryption, it is a best practice to encrypt everything.

3.1.1.2. Requirements

• BIG-IP LTM, web server, and a client workstation. In this lab, the Ubuntu client is the client workstation.

3.1.1.3. The iRule

when CLIENTSSL_HANDSHAKE {
    ISTATS::incr "ltm.virtual [virtual name] c [SSL::cipher version]" 1
}

3.1.1.4. Analysis

• iStats are user-created custom statistics, accessible from both the data plane (iRules) and the control plane (tmsh, on-box scripts, etc.). What we’re doing here is simply cataloging the SSL/TLS version from each client SSL handshake and storing these in an iStats table. That data can then be accessed from pretty much anywhere. For example, see David Holmes’ excellent guide on dumping this information to a Google pie chart:

  https://devcentral.f5.com/s/articles/categorize-ssl-traffic-by-version-display-as-graph

3.1.1.5. Testing

• Apply this iRule to the https virtual server:

  Connect to the TMUI of the BIGIP.
  Navigate to Local Traffic -> Virtual Servers and click on the https virtual server.
  Under the Resources tab, click Manage above the iRules section.
  Move the Lab1_1 iRule from Available to Enabled, and click Finished.
  

• Establish several connections to the virtual server from the Ubuntu client using different ciphers.

  openssl s_client -connect www.f5demolabs.com:443 <cipher>

  where cipher options could include {-tls1, -tls1_1, -tls1_2} to simulate different connections.

• At any point you can access the data collected in the iStats by simply typing the following at the BIG-IP command line:

  run \util bash
  istats dump
  

  Here’s an example output:

  [ ltm.virtual=/Common/stdsslvip ][TLSv1.1] = 54 (2015-09-01 13:52:20)
  [ ltm.virtual=/Common/stdsslvip ][TLSv1.2] = 282 (2015-09-01 13:52:20)
  [ ltm.virtual=/Common/stdsslvip ][TLSv1] = 32 (2015-09-01 13:52:20)
  

3.1.1.6. Bonus version

Now that you have a better idea of what protocols are being used on your site, you may now want to ease your customers into a better security posture than simply denying access with no warning. To do this, we’ll first test the SSL/TLS version. if it’s below our security threshold, we’ll redirect the user to another page or site to inform them that they need to upgrade their browser.

when HTTP_REQUEST {
    if { (( [SSL::cipher version] equals "TLSv1" ) or ( [SSL::cipher version] equals "SSLv3" )) and not ( [HTTP::uri] equals "/insecure.html" ) } {
        set redirect "https://www.f5demolabs.com/insecure.html"
        HTTP::respond 302 Location "${redirect}"
   }
}

You’re still allowing SSLv3 and TLSv1 at this point, which is definitely bad, but you’re not allowing access to the application for anything less than TLSv1.1.

Hint

1. Change client ssl cipher from DEFAULT to DEFAULT:SSLv3 by modifying the clientssl profile.
2. Use curl -vk -sslv3 https://www.f5demolabs.com:443 to connect
3. Move bonus version of irule, Lab1_2, to the selected list of iRules on the HTTPS virtual server
4. Try again to use curl -vk -sslv3 https://www.f5demolabs.com:443 to connect. It should now be redirected.

3.1.1.7. Lab Notes

• Use your computer's browser to manage the BIG-IP.
• The test site URL is https://www.f5demolabs.com. A hosts file entry is already applied to the Ubuntu client.

• Use a command line client to also test access:

  • curl -vk https://www.f5demolabs.com -[sslv3|tlsv1.0|tlsv1.1|tlsv1.2]
  • openssl s_client -connect www.f5demolabs.com:443 -[tls1|tls1_1|tls1_2]

• Three TLS version control iRules are provided. The first two are already deployed on the lab BIGIP, but manual entry is encouraged to improve familiarity and understanding:

  • Basic istats capture
  • Redirect to insecure page if TLSv1 or SSLv3
  • Provide David Holmes' iRules and access to the /sslversions URL.