I'll admit I'm still pretty green at a lot of this (lots of experience in
computers, little in Linux) and don't understand everything. But I'm trying
to learn, so please go easy on me :-)
I've been having a problem with dictionary hacker attempts on my system
(hundreds or even thousands a day), so I implemented the following rules:
# Kill ssh hackers - watch for more than 3 connection attempts in under
# 15 minutes seconds and reject for 24 hours
iptables -N SSH-EVIL
iptables -A SSH-EVIL -m recent --name badSSH --set -j LOG --log-level DEBUG
--log-prefix "evil SSH user: "
iptables -A SSH-EVIL -j REJECT
iptables -N SSH
iptables -A SSH -p tcp ! --syn -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A SSH -p tcp --syn -m recent --name badSSH --rcheck --seconds 86400
-j REJECT
iptables -A SSH -p tcp --syn -m recent --name sshconn --rcheck --seconds 900
--hitcount 3 -j SSH-EVIL
iptables -A SSH -p tcp --syn -m recent --name sshconn --set
iptables -A SSH -p tcp --syn -j ACCEPT
And something similar for ftp. These work well. But I'm also getting people
trying to break in via the POP interface (I'm using qpopper). So I tried the
following, which does not work:
iptables -N POP-EVIL
iptables -A POP-EVIL -m recent --name badPOP --set -j LOG --log-level DEBUG
--log-prefix "evil POP user: "
iptables -A POP-EVIL -j REJECT
iptables -N POP
iptables -A POP -p tcp -i eth0 --dport 110 ! --syn -m state --state
ESTABLISHED,RELATED -j ACCEPT
iptables -A POP -p tcp -i eth0 --dport 110 -m recent --name badPOP --rcheck
--seconds 86400 -j REJECT
iptables -A POP -p tcp -i eth0 --dport 110 -m recent --name popconn --rcheck
--seconds 900 --hitcount 5 -j POP-EVIL
iptables -A POP -p tcp -i eth0 --dport 110 -m recent --name popconn --set
iptables -A FTP -p tcp --syn -j ACCEPT
So my question is - what am I doing wrong in the POP interface, and how can I
stop it here, also.
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