[TOP TIP] firewalld and ipset (country blacklist)

In a previous post, I mentioned how to create an ipset blacklist. In recent versions of firewalld, the developers implemented support for ipset from within firewalld, thus there is no need to setup ipset separately. Here is a quick and easy way to create an IP/net blacklist by using the new firewall-cmd commands. At the same time I will demonstrate how to block entire countries from being able to access your server.

Create the blacklist:

firewall-cmd --permanent --new-ipset=blacklist --type=hash:net --option=family=inet --option=hashsize=4096 --option=maxelem=200000

* –permanent = use to make changes to the permanent configuration

  • –new-ipset = name of the new IP/net blacklist

  • –type = storage hash type, "net" is for subnets, while "ip" for individual ip addresses

  • –option=family = IPv4 or IPv6 network, inet is for IPv4

  • –option=hashsize = the initial hash size of the list

  • –option=maxelem = max number of elements

Download net blocks:

wget http://www.ipdeny.com/ipblocks/data/countries/all-zones.tar.gz
tar -vxzf all-zones.tar.gz

Choose which countries you would like to block, ipdeny.com provides net blocks by country. The above command will download all country zones together in one archive. Once extracted you should end up with various files, each named after a country, for example "cn.zone" for China. I can't tell you what to block, it all depends on what kind of service you provide and the location of your "real" requests. Personally, I run many major European sites and based on my logs, I block the following countries: ar bd bg br by cn co il in ir kp ly mn mu pa sd tw ua ro ru ve vn

After block the above countries, SPAM and hacking attempts dropped to nearly zero. Pretty much anything else comes via a European or American proxy, but that is easy to mitigate, once I file an abuse report to their network provider, the proxy is usually shut down rather quickly. While orchestrated and methodical hacks won't be mitigated by a simple country block list, everything else will be blocked, especially spam.

Populate the blacklist:

firewall-cmd --permanent --ipset=blacklist --add-entries-from-file=./cn.zone

The above command will load a country zone file to our blacklist. Make sure to change the path and filename to your chosen country zone file. You may also add individual IP addresses or net blocks by yourself, from the shell or by using a tool like fail2ban, with the following simple shell script (for example, save it as ~/bin/ban):

firewall-cmd --permanent --ipset=blacklist --add-entry=$1
firewall-cmd --ipset=blacklist --add-entry=$1

Run it like this:

ban 192.168.1.0/24

Redirect the blacklist to the drop zone

firewall-cmd --permanent --zone=drop --add-source=ipset:blacklist
firewall-cmd --reload

So far, we have created a blacklist and populated it with IP addresses and net blocks, but it is not blocking anything. In order to use our blacklist, we set it as a firewall "source", this means that anything that matches our blacklist will be redirected to a specific zone. Thus, by redirecting the blacklist to the "drop" zone, we effectively block all connections that match our blacklist. Simple and effective. The reload command at the end is needed to bring our permanent changes to the live/running firewall.

PS:

You may expand the above into a monthly script, run as a cron job, which clears the blacklist and re-downloads the list with the latest zones.

3 Replies

This guild is excellent and I have used it a few times. I am wondering if there is a way to whitelist 1 IP from a block that might be in the drop zone?

Since iptables rules are read from top to bottom, it might be possible to accomplish this by inserting (with -I) an ACCEPT rule for the IP you want to whitelist, to the top of your ruleset. For example:

sudo iptables -I INPUT -s 1.2.3.4 -j ACCEPT

What would you do if you want to exclusively use firewall-cmd for the whitelist?

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