on 6-4-2009 3:48 AM Noel Butler spake the following:
On Thu, 2009-06-04 at 12:16 +0200, henry ritzlmayr wrote:
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.
Verified with 1.1.6 as well, nice catch Henry.
1.1.15 gives me one log entry, but lists the number of failed login attemps;
Jun 4 10:16:56 mail dovecot: pop3-login: Aborted login (auth failed, 1 attempts): user=<username>, method=PLAIN, rip=192.168.1.19, lip=192.168.0.1 Jun 4 10:18:10 mail dovecot: pop3-login: Aborted login (auth failed, 2 attempts): user=<username>, method=PLAIN, rip=192.168.1.19, lip=192.168.0.1