Hi List,
optimizing the configuration on one of our servers (which was hit by a brute force attack on dovecot) showed an odd behavior.
Dovecot Version 1.0.7 (CentOS 5.2)
The short story: On one of our servers an attacker did a brute force attack on dovecot (pop3). Since the attacker closed and reopened the connection after every user/password combination the logs showed many lines like this: dovecot: pop3-login: Aborted login: user=<test>,......
The problem: If the attacker wouldn't have closed and reopened the connection no log would have been generated and he/she would have endless tries. Not even an iptables/hashlimit or fail2ban would have kicked in.
How to reproduce: telnet dovecot-server pop3 user test pass test1 user test pass test2 ... QUIT ->Only the last try gets logged.
If I enable auth_verbose every attempt gets logged, but if I read the docs correctly this option should only be used for figuring out why authentication isn't working.
Question: Is there any way to close the connection after the first wrong user/pass combination. So an attacker would be forced to reopen it? This would be perfect since an easy iptables/hashlimit would avoid such a brute force attack.
Any other Ideas? Henry