iblock

iblock is a program adding the client IP to a Packet Filter table.

It is meant to be used to block scanner connecting on unused ports.

Upon connection, the IP is added to a PF table and all established connections with this IP are killed. You need to use a PF bloking rule using the table.

How to use

Add a dedicated user

useradd -s /sbin/nologin _iblock

Configure doas

Add in /etc/doas.conf:

permit nopass _iblock cmd /sbin/pfctl

Configure packet filter

Use this in /etc/pf.conf, choose which ports will trigger the ban from the variable:

# services triggering a block
blocking_tcp="{ 21 23 53 111 135 137:139 445 1433 25565 5432 3389 3306 27019 }"

table <iblocked> persist

block in quick from <iblocked> label iblock
# iblock listens on port 2507
pass in quick on egress inet proto tcp to port $blocking_tcp rdr-to 127.0.0.1 port 2507
pass in quick on egress inet6 proto tcp to port $blocking_tcp rdr-to ::1 port 2507

Don't forget to reload the rules with pfctl -f /etc/pf.conf.

Use another table or port name by passing appropriate flags to iblock:

rcctl set iblock flags -t another_table_name -p 5373

Get some statistics

Done! You can see IP banned using pfctl -t iblocked -T show and iblock will send blocked addresses to syslog.

In the example I added a label to the block rule, you can use pfctl -s labels to view statistics from this rule, see documentation for column meaning.