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1. Changing the default sshd port number
In contrast to other well known services (ftp/mail/www) ssh server does not need to listen on the default port. It's being used by a fewer people, sometimes only you and changing the default port is yet another step in increasing your server security.I have been using fail2ban software for some time. It scans the logs for failed login attempts and bans the attacker's IP if he fails to login too many times.
However, after a few days my firewall was full of banned IPs (good day - 5/10 IPs, bad day - more than 20).
From now on my ssh server is always running on a non-standard IP.
The number of failed login attempts has greatly decreased and the automated attacks are no longer spamming my logs.
Some useful settings from /etc/ssh/sshd_config file:
[root@server ~]# egrep "^Port|^PermitRootLogin|^MaxAuth" /etc/ssh/sshd_config
Port 4321
PermitRootLogin no
MaxAuthTries 3
2. Logging incoming connections
Even with ssh daemon running on a different port you may find it useful to log all the connection attempts to it. You can catch it via following iptables rule:iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 4321 -j LOG --log-prefix "iptables: "
Which should be inserted before accepting the connection on ssh port.
Next if you're using rsyslogd you can filter all the messages starting with "iptables :" and put them into a separate file:
[root@server ~]# cat /etc/rsyslog.d/iptables.conf
:msg, startswith, "iptables: " -/var/log/iptables.log
& ~
[root@server ~]# service rsyslog restart
[root@server ~]# cat /var/log/iptables.log
Dec 16 18:39:41 server kernel: iptables: IN=eth0 OUT= MAC=00:1c:14:01:30:de:00:16:83:76:07:29:08:00 SRC=10.23.189.14 DST=20.40.50.101 LEN=60 TOS=0x00 PREC=0x00 TTL=54 ID=31528 DF PROTO=TCP SPT=44074 DPT=4321 WINDOW=29200 RES=0x00 SYN URGP=0
