9.2. Adding Your Own Rules

If you would like to create a rule yourself and use it with Suricata, this guide might be helpful.

Start creating a file for your rule. Use one of the following examples in your console/terminal window:

sudo nano local.rules
sudo vim local.rules

Write your rule, see Rules Format and save it.

Update the Suricata configuration file so your rule is included. Use one of the following examples:

sudo nano /etc/suricata/suricata.yaml
sudo vim /etc/suricata/suricata.yaml

and make sure your local.rules file is added to the list of rules:

default-rule-path: /usr/local/etc/suricata/rules

  - suricata.rules
  - /path/to/local.rules

Now, run Suricata and see if your rule is being loaded.

suricata -c /etc/suricata/suricata.yaml -i wlan0

If the rule failed to load, Suricata will display as much information as it has when it deemed the rule un-loadable. Pay special attention to the details: look for mistakes in special characters, spaces, capital characters, etc.

Next, check if your log-files are enabled in the Suricata configuration file suricata.yaml.

If you had to correct your rule and/or modify Suricata's YAML configuration file, you'll have to restart Suricata.

If you see your rule is successfully loaded, you can double check your rule by doing something that should trigger it.

By default, Suricata will log alerts to two places

  • eve.json

  • fast.log

These files will be located in the log output directory which is set by one of two methods:

  1. Suricata configuration file: see default-log-dir for the name of the directory

  2. Suricata command line: Using -l /path/to/log-dir creates log files in the named directory.

The following example assumes that the log directory is named /var/log/suricata

tail -f /var/log/suricata/fast.log

If you would make a rule like this:

alert http any any -> any any (msg:"Do not read gossip during work";
content:"Scarlett"; nocase; classtype:policy-violation; sid:1; rev:1;)

Your alert should look like this:

09/15/2011-16:50:27.725288  [**] [1:1:1] Do not read gossip during work [**]
[Classification: Potential Corporate Privacy Violation] [Priority: 1] {TCP} ->