Securing Splunk Free Version When Installed On Security Onion Server (or anywhere else)

This stroke of genius comes directly from the man behind Security Onion, @dougburks, and solves two problems, one serious the other functional. Splunk’s free version allows you to index up to 500 mb/day, but does limit some (even basic) capabilities, most important of which is disabling authentication. If you’re running Splunk free version on your Security Onion server and access the server remotely (from another workstation), I highly suggest you make this your standard access process. The instructions below work on Ubuntu distributions and if you followed Doug’s advice about using a Security Onion VM as your client, this should work perfectly as long as you haven’t configured the VM as a server.

The method can be used on a Windows or Linux client. The instructions below focus on Linux, but googling “windows ssh tunnel how to” should get you a good start. In the example below port 81 is the Splunk port. If you installed Splunk on a different port just replace 81 with it.

The approach uses an SSH tunnel and is really easy to setup. On your Security Onion/Splunk server you’ll want to make sure SSH is enabled in Uncomplicated Firewall (ufw).

sudo ufw status

You should see 22/tcp ALLOW in the results. If it says DENY, then enable it:

sudo ufw allow 22/tcp

Next configure ufw to block (yes I said block) Snorby, Squert and Splunk ports:

sudo ufw deny 81/tcp
sudo ufw deny 443/tcp
sudo ufw deny 3000/tcp

From a remote Linux host with openssh-client installed:

sudo ssh username@securityonion.example.com -L 81:localhost:81 -L
443:localhost:443 -L 3000:localhost:3000

Replace username with the Security Onion/Splunk server user and securityonion.example.com with the hostname or IP address of your Security Onion/Splunk server. This command essentially tells your client to pass anything destined to localhost ports 81, 443 or 3000 to your SO server on it’s localhost port 81, 443 or 3000 via the SSH tunnel. The command requires sudo due to accessing privileged ports, so you’ll be prompted for your local password then again for the remote SO server user’s password. After authentication, you’ll have an active SSH terminal session to the server.

Launch a web browser and browse to any of the following:

http://localhost:81 – Splunk
https://localhost:443 – SO Home/Squert
https://localhost:3000 – Snorby

It’s that simple.

If you recall I mentioned a “functional” advantage of using this approach. In the Security Onion for Splunk app, I provide links to Snorby and Squert, but unfortunately, the user must configure the urls to fit their environment if they access the tools remotely. The default config uses “localhost” as the server, so if you’re following, if you use the above method to access Splunk securely, the Snorby and Squert links work out of the box. =)

Thanks and hat tip to Doug for this little gem! I had to bite my lip whenever I recommended someone install the free version of Splunk due to the authentication limit, but now I don’t have to.

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