Snort - ArchWiki

# Snort

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From the project home page:

  Snort® is an open source network intrusion prevention and detection system (IDS/IPS) developed by Sourcefire. Combining the benefits of signature, protocol, and anomaly-based inspection, Snort is the most widely deployed IDS/IPS technology worldwide. With millions of downloads and nearly 400,000 registered users, Snort has become the de facto standard for IPS.

## Installation

Install snortAUR from the AUR.

## Configuration

The main configuration file is `/etc/snort/snort.conf`.

Read it carefully, as usual it is very well documented.

    ipvar HOME_NET        10.0.0.0/28           # Change to the subnet of your LAN.
    ipvar EXTERNAL_NET    !$HOME_NET
    ipvar DNS_SERVERS     $HOME_NET
    ipvar SMTP_SERVERS    $HOME_NET
    ipvar HTTP_SERVERS    $HOME_NET
    ipvar SQL_SERVERS     $HOME_NET
    ipvar TELNET_SERVERS  $HOME_NET
    portvar HTTP_PORTS      80
    portvar SHELLCODE_PORTS !80
    portvar ORACLE_PORTS    1521
    ipvar AIM_SERVERS     [64.12.24.0/24,64.12.25.0/24,64.12.26.14/24,64.12.28.0/24,64.12.29.0/24,64.12.161.0/
                         24,64.12.163.0/24,205.188.5.0/24,205.188.9.0/24]
    ipvar RULE_PATH       /etc/snort/rules
    ipvar HTTP_PORTS      80:5000               # For HTTPd's running on port 80 and 5000. Change appropriately
                                              # to the ports you are using on your LAN.
    config detection:   search-method lowmem  # If you're using a machine "with very limited resources".

At the bottom of the file, there is a list of includes. These define which rules you want to enforce. (Un)comment as you please. You should check that the corresponding file exists, as for me, none of the rules files were present.

    groupadd snort
    mkdir -p /var/log/snort
    useradd -g snort -d /var/log/snort snort
    chown -R snort:snort /var/log/snort

The factual accuracy of this article or section is disputed.

Reason: Under review -- I am not sure about this yet. (Discuss in Talk:Snort#)

Edit `/etc/conf.d/snort`:

    SNORT_ARGS="-u snort -g snort -l /var/log/snort -K ascii -c /etc/snort/snort.conf -D -h 10.0.0.0/28 -A full

Replace 10.0.0.0/28 with the CIDR of your LAN.

Now Snort will run as user snort in group snort. Should improve security. The other options make it log to `/var/log/snort` in ASCII mode. Run snort -h to see other available options.

I have been running my router for 12 days now, and using the above snort options, I had around 120MB of logs! So I changed the -A switch to "-A none". This only logs alerts. I did not know what to do with all the logs anyway.

## Update the rules: Oinkmaster

If you want to be able to download Snort's latest rules, you will need a subscription. This costs money. If you are happy enough with 5 days old rules, you just need to register for free. If you do not, the only updates you will get are the new rules distributed with a new Snort release. Go ahead and register at Snort. If you really do not want to register, you can use the rules from BleedingSnort.com. They are bleeding edge, meaning they have not been tested thoroughly.

oinkmasterAUR is available as AUR package.

### Oinkmaster setup

Edit `/etc/oinkmaster.conf` and look for the URL section and uncomment the 2.4 line. Make sure to replace <oinkcode> by the Oink code you generated after logging into your Snort account. For Bleeding Snort rules, uncomment the appropriate line.

When you log into your new account, create an "Oink code". Another thing to change is

    use_external_bins=1 # 1 uses wget, tar, gzip instead of Perl modules

The rest of the configuration file is fine.

### Oinkmaster usage

    oinkmaster.pl -o /etc/snort/rules

Create an executable script with the exact command and place it in /etc/cron.daily to update the rules daily automatically.

## See also

- Simple stateful firewall
- Router

Category:

- Security