IPTables配置Script(轉)

IPTables配置Script(轉)[@more@]

# ~jns/security/iptables/index.html

# Prepared by James C. Stephens

# (jns@gfdl.noaa.gov)

#!/bin/bash

#

# Load appropriate modules.

modprobe ip_tables

modprobe ip_conntrack

modprobe ip_conntrack_ftp

# These lines are here in case rules are already in place and the script is ever rerun on the fly.

# We want to remove all rules and pre-exisiting user defined chains and zero the counters

# before we implement new rules.

iptables -F

iptables -X

iptables -Z

# Set up a default DROP policy for the built-in chains.

# If we modify and re-run the script mid-session then (because we have a default DROP

# policy), what happens is that there is a small time period when packets are denied until

# the new rules are back in place. There is no period, however small, when packets we

# don't want are allowed.

iptables -P INPUT DROP

iptables -P FORWARD DROP

iptables -P OUTPUT DROP

## ===========================================================

## Some definitions:

NAMESERVER_1="x.x.x.x"

NAMESERVER_2="x.x.x.x"

BROADCAST="x.x.x.255"

LOOPBACK="127.0.0.0/8"

CLASS_A="10.0.0.0/8"

CLASS_B="172.16.0.0/12"

CLASS_C="192.168.0.0/16"

CLASS_D_MULTICAST="224.0.0.0/4"

CLASS_E_RESERVED_NET="240.0.0.0/5"

P_PORTS="0:1023"

UP_PORTS="1024:65535"

TR_SRC_PORTS="32769:65535"

TR_DEST_PORTS="33434:33523"

## ============================================================

## Kernel flags

# To dynamically change kernel parameters and variables on the fly you need

# CONFIG_SYSCTL defined in your kernel. I would advise the following:

# Disable response to ping.

/bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all

# Disable response to broadcasts.

# You don't want yourself becoming a Smurf amplifier.

/bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

# Don't accept source routed packets. Attackers can use source routing to generate

# traffic pretending to be from inside your network, but which is routed back along

# the path from which it came, namely outside, so attackers can compromise your

# network. Source routing is rarely used for legitimate purposes.

/bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_source_route

# Disable ICMP redirect acceptance. ICMP redirects can be used to alter your routing

# tables, possibly to a bad end.

/bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_redirects

# Enable bad error message protection.

/bin/echo "1" > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses

# Turn on reverse path filtering. This helps make sure that packets use

# legitimate source addresses, by automatically rejecting incoming packets

# if the routing table entry for their source address doesn't match the network

# interface they're arriving on. This has security advantages because it prevents

# so-called IP spoofing, however it can pose problems if you use asymmetric routing

# (packets from you to a host take a different path than packets from that host to you)

# or if you operate a non-routing host which has several IP addresses on different

# interfaces. (Note - If you turn on IP forwarding, you will also get this).

for interface in /proc/sys/net/ipv4/conf/*/rp_filter; do

/bin/echo "1" > ${interface}

done

# Log spoofed packets, source routed packets, redirect packets.

/bin/echo "1" > /proc/sys/net/ipv4/conf/all/log_martians

# Make sure that IP forwarding is turned off. We only want this for a multi-homed host.

/bin/echo "0" > /proc/sys/net/ipv4/ip_forward

# Note: With connection tracking, all fragments are reassembled before being

# passed to the packet-filtering code so there is no ip_always_defrag switch as there

# was in the 2.2 kernel.

## ============================================================

# RULES

## LOOPBACK

# Allow unlimited traffic on the loopback interface.

iptables -A INPUT -i lo -j ACCEPT

iptables -A OUTPUT -o lo -j ACCEPT

## SYN-FLOODING PROTECTION

# This rule maximises the rate of incoming connections. In order to do this we divert tcp

# packets with the SYN bit set off to a user-defined chain. Up to limit-burst connections

# can arrive in 1/limit seconds ..... in this case 4 connections in one second. After this, one

# of the burst is regained every second and connections are allowed again. The default limit

# is 3/hour. The default limit burst is 5.

#

iptables -N syn-flood

iptables -A INPUT -i $IFACE -p tcp --syn -j syn-flood

iptables -A syn-flood -m limit --limit 1/s --limit-burst 4 -j RETURN

iptables -A syn-flood -j DROP

## Make sure NEW tcp connections are SYN packets

iptables -A INPUT -i $IFACE -p tcp ! --syn -m state --state NEW -j DROP

## FRAGMENTS

# I have to say that fragments scare me more than anything.

# Sending lots of non-first fragments was what allowed Jolt2 to effectively "drown"

# Firewall-1. Fragments can be overlapped, and the subsequent interpretation of such

# fragments is very OS-dependent (see this paper for details).

# I am not going to trust any fragments.

# Log fragments just to see if we get any, and deny them too.

iptables -A INPUT -i $IFACE -f -j LOG --log-prefix "IPTABLES FRAGMENTS: "

iptables -A INPUT -i $IFACE -f -j DROP

## SPOOFING

# Most of this anti-spoofing stuff is theoretically not really necessary with the flags we

# have set in the kernel above ........... but you never know there isn't a bug somewhere in

# your IP stack.

#

# Refuse spoofed packets pretending to be from your IP address.

iptables -A INPUT -i $IFACE -s $IPADDR -j DROP

# Refuse packets claiming to be from a Class A private network.

iptables -A INPUT -i $IFACE -s $CLASS_A -j DROP

# Refuse packets claiming to be from a Class B private network.

iptables -A INPUT -i $IFACE -s $CLASS_B -j DROP

# Refuse packets claiming to be from a Class C private network.

iptables -A INPUT -i $IFACE -s $CLASS_C -j DROP

# Refuse Class D multicast addresses. Multicast is illegal as a source address.

iptables -A INPUT -i $IFACE -s $CLASS_D_MULTICAST -j DROP

# Refuse Class E reserved IP addresses.

iptables -A INPUT -i $IFACE -s $CLASS_E_RESERVED_NET -j DROP

# Refuse packets claiming to be to the loopback interface.

# Refusing packets claiming to be to the loopback interface protects against

# source quench, whereby a machine can be told to slow itself down by an icmp source

# quench to the loopback.

iptables -A INPUT -i $IFACE -d $LOOPBACK -j DROP

# Refuse broadcast address packets.

iptables -A INPUT -i $IFACE -d $BROADCAST -j DROP

## DNS

# NOTE: DNS uses tcp for zone transfers, for transfers greater than 512 bytes (possible, but unusual), and on certain

# platforms like AIX (I am told), so you might have to add a copy of this rule for tcp if you need it

# Allow UDP packets in for DNS client from nameservers.

iptables -A INPUT -i $IFACE -p udp -s $NAMESERVER_1 --sport 53 -m state --state ESTABLISHED -j ACCEPT

iptables -A INPUT -i $IFACE -p udp -s $NAMESERVER_2 --sport 53 -m state --state ESTABLISHED -j ACCEPT

# Allow UDP packets to DNS servers from client.

iptables -A OUTPUT -o $IFACE -p udp -d $NAMESERVER_1 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p udp -d $NAMESERVER_2 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT

## SSH

# Allow ssh outbound.

iptables -A INPUT -i $IFACE -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT

## WWW

# Allow www outbound to 80.

iptables -A INPUT -i $IFACE -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT

# Allow www outbound to 443.

iptables -A INPUT -i $IFACE -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT

## TELNET

# Allow telnet outbound.

iptables -A INPUT -i $IFACE -p tcp --sport 23 -m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 23 -m state --state NEW,ESTABLISHED -j ACCEPT

## FTP

# Allow ftp outbound.

iptables -A INPUT -i $IFACE -p tcp --sport 21 -m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 21 -m state --state NEW,ESTABLISHED -j ACCEPT

# Now for the connection tracking part of ftp. This is discussed more completely in my section

# on connection tracking to be found here.

# 1) Active ftp.

# This involves a connection INbound from port 20 on the remote machine, to a local port

# passed over the ftp channel via a PORT command. The ip_conntrack_ftp module recognizes

# the connection as RELATED to the original outgoing connection to port 21 so we don't

# need NEW as a state match.

iptables -A INPUT -i $IFACE -p tcp --sport 20 -m state --state ESTABLISHED,RELATED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 20 -m state --state ESTABLISHED -j ACCEPT

# 2) Passive ftp.

# This involves a connection outbound from a port >1023 on the local machine, to a port >1023

# on the remote machine previously passed over the ftp channel via a PORT command. The

# ip_conntrack_ftp module recognizes the connection as RELATED to the original outgoing

# connection to port 21 so we don't need NEW as a state match.

iptables -A INPUT -i $IFACE -p tcp --sport $UP_PORTS --dport $UP_PORTS

-m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --sport $UP_PORTS --dport $UP_PORTS

-m state --state ESTABLISHED,RELATED -j ACCEPT

## SMTP

# Allow smtp outbound.

iptables -A INPUT -i $IFACE -p tcp --sport 25 -m state --state ESTABLISHED -j ACCEPT

iptables -A OUTPUT -o $IFACE -p tcp --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT

## AUTH server

# Reject ident probes with a tcp reset.

# I need to do this for a broken mailhost that won't accept my mail if I just drop its ident probe.

iptables -A INPUT -i $IFACE -p tcp --dport 113 -j REJECT --reject-with tcp-reset

## TRACEROUTE

# Outgoing traceroute anywhere.

# The reply to a traceroute is an icmp time-exceeded which is dealt with by the next rule.

iptables -A OUTPUT -o $IFACE -p udp --sport $TR_SRC_PORTS --dport $TR_DEST_PORTS

-m state --state NEW -j ACCEPT

# ICMP

# We accept icmp in if it is "related" to other connections (e.g a time exceeded (11)

# from a traceroute) or it is part of an "established" connection (e.g. an echo reply (0)

# from an echo-request (8)).

iptables -A INPUT -i $IFACE -p icmp -m state --state ESTABLISHED,RELATED -j ACCEPT

# We always allow icmp out.

iptables -A OUTPUT -o $IFACE -p icmp -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

## LOGGING

# You don't have to split up your logging like I do below, but I prefer to do it this way

# because I can then grep for things in the logs more easily. One thing you probably want

# to do is rate-limit the logging. I didn't do that here because it is probably best not too

# when you first set things up ................. you actually really want to see everything going to

# the logs to work out what isn't working and why. You cam implement logging with

# "-m limit --limit 6/h --limit-burst 5" (or similar) before the -j LOG in each case.

#

# Any udp not already allowed is logged and then dropped.

iptables -A INPUT -i $IFACE -p udp -j LOG --log-prefix "IPTABLES UDP-IN: "

iptables -A INPUT -i $IFACE -p udp -j DROP

iptables -A OUTPUT -o $IFACE -p udp -j LOG --log-prefix "IPTABLES UDP-OUT: "

iptables -A OUTPUT -o $IFACE -p udp -j DROP

# Any icmp not already allowed is logged and then dropped.

iptables -A INPUT -i $IFACE -p icmp -j LOG --log-prefix "IPTABLES ICMP-IN: "

iptables -A INPUT -i $IFACE -p icmp -j DROP

iptables -A OUTPUT -o $IFACE -p icmp -j LOG --log-prefix "IPTABLES ICMP-OUT: "

iptables -A OUTPUT -o $IFACE -p icmp -j DROP

# Any tcp not already allowed is logged and then dropped.

iptables -A INPUT -i $IFACE -p tcp -j LOG --log-prefix "IPTABLES TCP-IN: "

iptables -A INPUT -i $IFACE -p tcp -j DROP

iptables -A OUTPUT -o $IFACE -p tcp -j LOG --log-prefix "IPTABLES TCP-OUT: "

iptables -A OUTPUT -o $IFACE -p tcp -j DROP

# Anything else not already allowed is logged and then dropped.

# It will be dropped by the default policy anyway ........ but let's be paranoid.

iptables -A INPUT -i $IFACE -j LOG --log-prefix "IPTABLES PROTOCOL-X-IN: "

iptables -A INPUT -i $IFACE -j DROP

iptables -A OUTPUT -o $IFACE -j LOG --log-prefix "IPTABLES PROTOCOL-X-OUT: "

iptables -A OUTPUT -o $IFACE -j DROP