Snort.conf to Suricata.yaml

This guide is meant for those who are familiar with Snort and the snort.conf configuration format. This guide will provide a 1:1 mapping between Snort and Suricata configuration whereever possible.

Variables

snort.conf

ipvar HOME_NET any
ipvar EXTERNAL_NET any
...

portvar HTTP_PORTS [80,81,311,591,593,901,1220,1414,1741,1830,2301,2381,2809,3128,3702,4343,4848,5250,7001,7145,7510,7777,7779,8000,8008,8014,8028,8080,8088,8090,8118,8123,8180,8181,8243,8280,8800,8888,8899,9000,9080,9090,9091,9443,9999,11371,55555]
portvar SHELLCODE_PORTS !80
...

suricata.yaml

vars:
  address-groups:

    HOME_NET: "[192.168.0.0/16,10.0.0.0/8,172.16.0.0/12]" 
    EXTERNAL_NET: "!$HOME_NET" 

  port-groups:
    HTTP_PORTS: "80" 
    SHELLCODE_PORTS: "!80" 

Note that Suricata can automatically detect HTTP traffic regardless of the port it uses. So the HTTP_PORTS variable is not nearly as important as it is with Snort, if you use a Suricata enabled ruleset.

Decoder alerts

snort.conf

# Stop generic decode events:
config disable_decode_alerts

# Stop Alerts on experimental TCP options
config disable_tcpopt_experimental_alerts

# Stop Alerts on obsolete TCP options
config disable_tcpopt_obsolete_alerts

# Stop Alerts on T/TCP alerts
config disable_tcpopt_ttcp_alerts

# Stop Alerts on all other TCPOption type events:
config disable_tcpopt_alerts

# Stop Alerts on invalid ip options
config disable_ipopt_alerts

suricata.yaml

Suricata has no specific decoder options. All decoder related alerts are controlled by rules. See #Rules below.

Checksum handling

snort.conf

config checksum_mode: all

suricata.yaml

Suricata's checksum handling works on-demand. The stream engine checks TCP and IP checksum by default:

stream:
  checksum-validation: yes      # reject wrong csums

Alerting on bad checksums can be done with normal rules. See #Rules, decoder-events.rules specifically.

Various configs

Active response

snort.conf

# Configure active response for non inline operation. For more information, see REAMDE.active
# config response: eth0 attempts 2

suricata.yaml

Active responses are handled automatically w/o config if rules with the "reject" action are used.

Dropping privileges

snort.conf

# Configure specific UID and GID to run snort as after dropping privs. For more information see snort -h command line options
#
# config set_gid:
# config set_uid:

Suricata

To set the user and group use the --user <username> and --group <groupname> commandline options.

Snaplen

snort.conf

# Configure default snaplen. Snort defaults to MTU of in use interface. For more information see README
#
# config snaplen:
#

Suricata always works at full snap length to provide full traffic visibility.

Bpf

snort.conf

# Configure default bpf_file to use for filtering what traffic reaches snort. For more information see snort -h command line options (-F)
#
# config bpf_file:
#

suricata.yaml

BPF filters can be set per packet acquisition method, with the "bpf-filter: <file>" yaml option and in a file using the -F command line option.

For example:

pcap:
  - interface: eth0
    #buffer-size: 16777216
    #bpf-filter: "tcp and port 25" 
    #checksum-checks: auto
    #threads: 16
    #promisc: no
    #snaplen: 1518

Log directory

snort.conf

# Configure default log directory for snort to log to.  For more information see snort -h command line options (-l)
#
# config logdir:


suricata.yaml
default-log-dir: /var/log/suricata/

This value is overridden by the -l commandline option.

Packet acquisition

snort.conf

# Configure DAQ related options for inline operation. For more information, see README.daq
#
# config daq: <type>
# config daq_dir: <dir>
# config daq_mode: <mode>
# config daq_var: <var>
#
# <type> ::= pcap | afpacket | dump | nfq | ipq | ipfw
# <mode> ::= read-file | passive | inline
# <var> ::= arbitrary <name>=<value passed to DAQ
# <dir> ::= path as to where to look for DAQ module so's

suricata.yaml

Suricata has all packet acquisition support built-in. It's configuration format is very verbose.

pcap:
  - interface: eth0
    #buffer-size: 16777216
    #bpf-filter: "tcp and port 25" 
    #checksum-checks: auto
    #threads: 16
    #promisc: no
    #snaplen: 1518
pfring:
afpacket:
nfq:
ipfw:

Passive vs inline vs reading files is determined by how Suricata is invoked on the command line.

Rules

snort.conf:

In snort.conf a RULE_PATH variable is set, as well as variables for shared object (SO) rules and preprocessor rules.

var RULE_PATH ../rules
var SO_RULE_PATH ../so_rules
var PREPROC_RULE_PATH ../preproc_rules

include $RULE_PATH/local.rules
include $RULE_PATH/emerging-activex.rules
...

suricata.yaml:

In the suricata.yaml the default rule path is set followed by a list of rule files. Suricata does not have a concept of shared object rules or preprocessor rules. Instead of preprocessor rules, Suricata has several rule files for events set by the decoders, stream engine, http parser etc.

default-rule-path: /etc/suricata/rules
rule-files:
 - local.rules
 - emerging-activex.rules

The equivalent of preprocessor rules are loaded like normal rule files:

rule-files:
 - decoder-events.rules
 - stream-events.rules
 - http-events.rules
 - smtp-events.rules