Re: please read my script

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• In reply to: NeoSadist: "please read my script"
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Date: 20 Nov 2003 11:06:17 -0600

NeoSadist wrote:

>Please read my IPTables script (for a home computer) and tell me what you
>think. All ideas/comments accepted:
>
># Accept all loopback
>iptables -A INPUT -i lo -p all -j ACCEPT
>iptables -A OUTPUT -o lo -p all -j ACCEPT

Since you don't flush your rules, or set default policies, the above
is unnecessary. Your iptables obviously accepts all by default.

<snip chat rules>

># Close all other connection requests
># All rules for accepting connections should be entered before this rule.
>iptables -A INPUT -p tcp --syn -j DROP

Unfortunately, you are *not* closing all other connection requests.
All ICMP and UDP are allowed. Not a good thing, IMHO. Also, you are
limiting the TCP packets to be dropped. A classic example of a very
permissive firewall ruleset. All output is allowed as well.

Iptables/netfilter is a very robust and feature-rich firewall, and
your ruleset isn't taking advantage of a lot of it. Try this command:
iptables -L and you'll see how permissive it is. And I thought mine
was rather permissive. Mind you, I'm behind a Linux firewall/router
with a ruleset greater than 30K and nothing is forwarded to this
computer except what is used by NAT.

#!/bin/bash
#
modprobe ip_tables
modprobe ip_conntrack
modprobe ip_conntrack_ftp
# Flush Chains
iptables -F
iptables -X
iptables -Z
# Set Policies
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# Allow Loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# Input Rules
iptables -A INPUT -i eth0 -p tcp --dport 21 -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 20 -j ACCEPT
iptables -A INPUT -i eth0 -p udp --dport 67:68 -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --dport 113 -j REJECT \
--reject-with tcp-reset
iptables -A INPUT -i eth0 -p udp --sport 137:139 -j DROP
iptables -A INPUT -i eth0 -p icmp -j ACCEPT
iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED \
-j ACCEPT
# Output Rules
iptables -A OUTPUT -o eth0 -p tcp --dport 20 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 21 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 22 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 23 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 25 -j ACCEPT
iptables -A OUTPUT -o eth0 -p udp --dport 43 -j ACCEPT
iptables -A OUTPUT -o eth0 -p udp --dport 53 -j ACCEPT
iptables -A OUTPUT -o eth0 -p udp --dport 67:68 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 80 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 110 -j ACCEPT
iptables -A OUTPUT -o eth0 -p udp --dport 123 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 119 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 443 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 3128 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 8080 -j ACCEPT
iptables -A OUTPUT -o eth0 -p icmp -j ACCEPT
iptables -A OUTPUT -o eth0 -m state --state ESTABLISHED,RELATED \
-j ACCEPT
# Log and Drop Everything Else
iptables -A INPUT -j LOG
iptables -A INPUT -j DROP
iptables -A FORWARD -j LOG
iptables -A FORWARD -j DROP
iptables -A OUTPUT -j LOG
iptables -A OUTPUT -j DROP

• Previous message: Knutts: "ARP Broadcast From CISCO PIX Firewall"
• In reply to: NeoSadist: "please read my script"
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