## Shorewall Blacklisting/Whitelisting Support

### Tom Eastep

Copyright © 2002-2006, 2010, 2011 Thomas M. Eastep

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

2020/09/24

### Caution

This article applies to Shorewall 4.4 and later. If you are running a version of Shorewall earlier than Shorewall 4.3.5 then please see the documentation for that release.

## Introduction

Shorewall supports two different types of blacklisting; rule-based, static and dynamic. The BLACKLIST option in /etc/shorewall/shorewall.conf controls the degree of blacklist filtering.

The BLACKLIST option lists the Netfilter connection-tracking states that blacklist rules are to be applied to (states are NEW, ESTABLISHED, RELATED, INVALID, NOTRACK). The BLACKLIST option supersedes the BLACKLISTNEWONLY option:

1. BLACKLISTNEWONLY=No -- All incoming packets are checked against the blacklist. New blacklist entries can be used to terminate existing connections.

2. BLACKLISTNEWONLY=Yes -- The blacklists are only consulted for new connection requests. Blacklists may not be used to terminate existing connections.

### Important

For automatic blacklisting based on exceeding defined threshholds, see Events.

## Rule-based Blacklisting

Beginning with Shorewall 4.4.25, the preferred method of blacklisting and whitelisting is to use the blrules file (shorewall-blrules (5)). There you have access to the DROP, ACCEPT, REJECT and WHITELIST actions, standard and custom macros as well as standard and custom actions. See shorewall-blrules (5) for details.

Example:

    #ACTION         SOURCE                  DEST                    PROTO   DPORT

    WHITELIST       net:70.90.191.126       all
    DROP            net                     all                     udp     1023:1033,1434,5948,23773
    DROP            all                     net                     udp     1023:1033
    DROP            net                     all                     tcp     57,1433,1434,2401,2745,3127,3306,3410,4899,5554,5948,6101,8081,9898,23773
    DROP            net:221.192.199.48      all
    DROP            net:61.158.162.9        all
    DROP            net:81.21.54.100        all                     tcp     25
    DROP            net:84.108.168.139      all
    DROP            net:200.55.14.18        all

Beginning with Shorewall 4.4.26, the update command supports a `-b` option that causes your legacy blacklisting configuration to use the blrules file.

## Chain-based Dynamic Blacklisting

Beginning with Shorewall 4.4.7, dynamic blacklisting is enabled by setting DYNAMIC_BLACKLIST=Yes in `shorewall.conf`. Prior to that release, the feature is always enabled.

Once enabled, dynamic blacklisting doesn't use any configuration parameters but is rather controlled using /sbin/shorewall[-lite] commands. Note that to and from may only be specified when running Shorewall 4.4.12 or later.

- drop [to|from] <ip address list> - causes packets from the listed IP addresses to be silently dropped by the firewall.

- reject [to|from]<ip address list> - causes packets from the listed IP addresses to be rejected by the firewall.

- allow [to|from] <ip address list> - re-enables receipt of packets from hosts previously blacklisted by a drop or reject command.

- save - save the dynamic blacklisting configuration so that it will be automatically restored the next time that the firewall is restarted.

  Update: Beginning with Shorewall 4.4.10, the dynamic blacklist is automatically retained over stop/start sequences and over restart and reload.

- show dynamic - displays the dynamic blacklisting configuration.

- logdrop [to|from] <ip address list> - causes packets from the listed IP addresses to be dropped and logged by the firewall. Logging will occur at the level specified by the BLACKLIST_LOGLEVEL setting at the last [re]start (logging will be at the 'info' level if no BLACKLIST_LOGLEVEL was given).

- logreject [to|from}<ip address list> - causes packets from the listed IP addresses to be rejected and logged by the firewall. Logging will occur at the level specified by the BLACKLIST_LOGLEVEL setting at the last [re]start (logging will be at the 'info' level if no BLACKLIST_LOGLEVEL was given).

## Ipset-based Dynamic Blacklisting

Beginning with Shorewall 5.0.8, it is possible to use an ipset to hold blacklisted addresses. The DYNAMIC_BLACKLIST option was expanded to:

DYNAMIC_BLACKLIST={Yes|No||ipset[-only][`,option`[,...]][:[`setname`][:`log_level`|:l`og_tag`]]]}

When `ipset` or `ipset-only` is specified, the shorewall blacklist command is used to blacklist a single host or a network. The allow command is used to remove entries from the ipset. The name of the set (`setname`) and the level (`log_level`), if any, at which blacklisted traffic is to be logged may also be specified. The default set name is SW_DBL4 and the default log level is `none` (no logging). If `ipset-only` is given, then chain-based dynamic blacklisting is disabled just as if DYNAMIC_BLACKLISTING=No had been specified.

Possible `option`s are:

src-dst

  Normally, only packets whose source address matches an entry in the ipset are dropped. If `src-dst` is included, then packets whose destination address matches an entry in the ipset are also dropped.

`disconnect`

  The `disconnect` option was added in Shorewall 5.0.13 and requires that the conntrack utility be installed on the firewall system. When an address is blacklisted using the blacklist command, all connections originating from that address are disconnected. if the `src-dst` option was also specified, then all connections to that address are also disconnected.

`timeout`=`seconds`

  Added in Shorewall 5.0.13. Normally, Shorewall creates the dynamic blacklisting ipset with timeout 0 which means that entries are permanent. If you want entries in the set that are not accessed for a period of time to be deleted from the set, you may specify that period using this option. Note that the blacklist command can override the ipset's timeout setting.

  ### Important

  Once the dynamic blacklisting ipset has been created, changing this option setting requires a complete restart of the firewall; shorewall restart if RESTART=restart, otherwise shorewall stop && shorewall start

log

  Added in Shorewall 5.2.5. When specified, successful 'blacklist' and 'allow' commands will log a message to the system log.

noupdate

  Added in Shorewall 5.2.5. Normally, once an address has been blacklisted, each time that a packet is received from the packet, the ipset's entry for the address is updated to reset the timeout to the value specifyed in the `timeout` option above. Setting the `noupdate` option, inhibits this resetting of the entry's timeout. This option is ignored when the `timeout` option is not specified.

When ipset-based dynamic blacklisting is enabled, the contents of the blacklist will be preserved over stop/reboot/start sequences.

## BLACKLIST Policy and Action

Beginning with Shorewall 5.1.1, it is possible to specify BLACKLIST in the POLICY column of shorewall-policy(5) when ipset-based dynamic blacklisting is being used. When a packet is disposed of via the BLACKLIST policy, the packet's sender is added to the dynamic blacklist ipset and the packet is dropped.

Also available beginning with Shorewall 5.1.1 is a BLACKLIST action for use in the rules file, macros and filter table actions. Execute the shorewall show action BLACKLIST command for details.

## BLACKLIST and Fail2ban

The BLACKLIST command can be used as 'blocktype' in /etc/fail2ban/actions.d/shorewall.conf. Prior to Shorewall 5.2.5, this works best if there is no timeout specified in the DYNAMIC_BLACKLIST setting or if timeout=0 is given.

Beginning with Shorewall 5.2.5, Shorewall includes new features that allow fail2ban to work most seamlessly with Shorewall's ipset-based dynamic blacklisting:

- When a timeout is specified in the DYNAMIC_BLACKLIST setting, the dynamic-blacklisting ipset is created with default timeout 0. As entries are added by BLACKLIST policies or by the blacklist command, the created entry is given the specified timeout value.

- The noupdate option has been added. Specifying this option prevents 'timeout 0' ipset entries from being changed to finite timeout entries as a result of blacklisted ip addresses continuing to send packets to the firewall.

- The blacklist! command has been added. specifying that command as the fail2ban 'blocktype' causes entries created by fail2ban to persist until fail2ban unbans them using the Shorewall allow comand.

There are a couple of additional things to note:

- The documentation in /etc/fail2ban/action.d/shorewall.conf states that you should set BLACKLIST=All. A better approach when using BLACKLIST as the 'blocktype' is to specify the disconnect option in the setting of DYNAMIC_BLACKLIST. With BLACKLIST=All, every packet entering the firewall from the net must be checked against the dynamic-blacklisting ipset. That is not required when you specify disconnect.

- The noupdate option allows fail2ban full control when a host is 'unbanned'. The cost of using this option is that after the specified timeout, the entry for an attacking host will be removed from the dynamic-blacklisting ipset, even if the host has continued the attack while blacklisted. This isn't a great concern, as the first attempt to access an unauthorized service will result in the host being re-blacklisted.