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====== PFSense - Suricata - Rules - Breakdown of a rule ======

===== Example Rule =====

<code snort>
alert ip any any -> any any (msg:"IP detected"; sid:2; rev:1;)
</code>

where

  * **alert**:  The action to perform on the rule.
  * **ip**:  The protocol that the rule will match.  When ip is specified it will watch for all or any packets on the network involving the adapter.
  * **any any -> any any**:  Source IP and Port; Direction; Destination IP and Port.
  * **(msg:"ICMP detected"; sid:2; rev:1;)**:  The options.

----

<WRAP info>
**NOTE:**  Aliases can also be used.

<code snort>
alert ip $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"IP detected"; sid:2; rev:1;)
</code>

where:

  * **$HOME_NET**:  An alias of internal IPs.
  * **$EXTERNAL_NET**:  An alias of non HOME_NET.
  * **$HTTP_PORTS**:  An alias of ports.

</WRAP>


----

===== Actions =====

Actions are performed in the following precedence order by default if multiple rules exist; but can be changed through Action Order.

  * **pass**:  If the packet matches this rule it will be accepted through.
  * **drop**:  The packet will be silently removed from the network stack.  An alert will be generated as well.
  * **reject**:  This acts the same as drop but will also notify the sender that the packet has been removed from the stack.
  * **alert**: - Just notifies of any packets that have matched rules.

----

===== Protocol ====

  * **ip**:  Any packets on the network involving the adapter.
  * **tcp**:  TCP.
  * **udp**:  UDP.
  * **icm**:  ICMP packets, such as ping.

<WRAP info>
**NOTE:** Suricata also allows you to specify layer 7 protocols as well, such as HTTP (http), SSL and TLS (tls for both), FTP (ftp) and SMB (smb).
</WRAP>

----

===== Source IP and Port; Direction; Destination IP and Port =====

<code>
any any -> any any
</code>

Source and Destination IP can be configured as:

  * **any**:  Any IP.
  * **192.168.1.10**:  An actual IP.
  * **10.0.1.0/8**:  A CIDR in the 10.0.1.0 subnet.
  * **!192.168.1.10**:  An exclamation mark specifies “not”, so this means any IP but not 192.168.1.10.
  * **!10.0.1.0/8**:  Any IP not in the 10.0.1.0 subnet.
  * **[192.168.1.10, !192.168.1.10]**:  Multiple addresses.  You can also mix-and-match with the ! as well.
  * **[$EXTERNAL_NET, !$HOME_NET]**:  Multiple addresses, using built-in variables.
  * **![192.168.1.0/24,192.168.0.0/24]**:  Not with Multiple addresses.

Ports act similarly:

  * **any**:  Any Port.
  * **80**:  Port 80.
  * **[80:85]**:  A range of ports.
  * **[:1024]**:  Matches all ports from 0-1024.
  * **[1024:]**:  Matches ports from 1024 to the highest (typically 65535).


Direction Specification:

  *  **<nowiki>-></nowiki>**:  This is the most common and means only check if the source IP and port are coming in to the destination IP and port.
  *  **<>**:  This will match packet flow in either direction.

<WRAP info>
**NOTE:**  Built-in Variables include:

  * **HOME_NET**:
  * **EXTERNAL_NET**:
</WRAP>


----

===== Rule Options =====

Options fall into different categories:

  * **[[https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Meta-settings|meta-settings]]**:  Options not pertaining to any specifics about the packet; including msg, sid, rev.
  * **[[https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Payload_keywords|payload]]**:  The packet data itself.  **content: "peter";**.
  * **[[https://redmine.openinfosecfoundation.org/projects/suricata/wiki/HTTP-keywords|HTTP]]**:  Heavily used when TCP protocol is set, useful for using Suricata as a content filtering system.  **GET, POST, index.html, cookies, user-agents, response-status 302, 500 etc.**.
  * **[[https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Flow-keywords|flow]]**:  More fine-grained control over the connection’s status and such.  **established, memory usage, timeouts, user logged in**.
  * **[[https://redmine.openinfosecfoundation.org/projects/suricata/wiki/IPReputationRules|IP reputation]]**:   Is an IP legit or known to be associated with malware, spam, etc...

----

<code>
msg:"IP detected"; sid:2; rev:1;
</code>

  * The 3 most basic options are:

  * **msg**: - What will be prompted in an alert (unless you’re using pass as the action, set this regardless).
  * **sid**: - This is a unique ID for the rule.
    * If multiple rules have the same sid Suricata will let you know, and not be nice about it.
    * Typically you should pick a really high number (> 100000) if you are going to write your own.
  * **rev**: - Revision number/ID.
    *  Incremented by 1 every time the rule is changed.


----

==== Other Rule Examples ====

<code>
alert icmp any any -> \
      any any (msg:"PING detected"; \
      sid:2; rev:1;)


alert tcp any any <> \
      any any (pcre:"/3\d{3}\
      (\s|-)?\d{6}(\s|-)?\d{5}/";\
      msg:"American Express card number \
      detected in clear text";content: \
      "amex";nocase;sid: 9000003;rev:1;)


alert tcp 1.2.3.4 1024 - > 5.6.7.8 80


# Detect SSH protocol anomalies.
alert tcp any any -> any 22 (msg:"ALERT TCP port 22 but not SSH"; app-layer-protocol:!ssh; sid:2271009; rev:1;)


# Non-TLS traffic on TLS ports.
alert tcp any any -> any [443,465] (msg:"Detected non-TLS on TLS port"; flow:to_server; app-layer-protocol:!tls; threshold: type limit, track by_src, seconds 90, count 1; sid:210003; rev:1;)


alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:\".htpasswd access attempt\"; flow:to_server,established; content:\".htpasswd\"; nocase; sid:210503; rev:1;)

</code>

----