A bash script for iptables dropping IPs which logged in failed more than 9 times.

drop.iptables

#!/usr/bin/env bash

lastb -if /var/log/btmp.1 | awk '{print$3}' | sort | uniq -cd > lastb.log.1
lastb -i | awk '{print$3}' | sort | uniq -cd > lastb.log

cat lastb.log.1 lastb.log | sort -n | awk '$1>9{print$2}' | sort -n > try9s.ip
echo '===== IPs failed more than 9 times ====='
cat try9s.ip

while read ip; do
    iptables --check INPUT --source $ip --jump DROP 2>/dev/null ||\
        iptables --append INPUT --source $ip --jump DROP
done < try9s.ip