iptables.v4.rules

*filter

# Base policy
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]

# Don't attempt to firewall internal traffic on the loopback device.
-A INPUT -i lo -j ACCEPT

# Continue connections that are already established or related to an established 
# connection.
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

# Drop non-conforming packets, such as malformed headers, etc.
-A INPUT -m conntrack --ctstate INVALID -j DROP

# Block remote packets claiming to be from a loopback address.
-A INPUT -s 127.0.0.0/8 ! -i lo -j DROP

# Drop all packets that are going to broadcast, multicast or anycast address.
-A INPUT -m addrtype --dst-type BROADCAST -j DROP
-A INPUT -m addrtype --dst-type MULTICAST -j DROP
-A INPUT -m addrtype --dst-type ANYCAST -j DROP
-A INPUT -d 224.0.0.0/4 -j DROP

# Chain for preventing SSH brute-force attacks.
# Permits 10 new connections within 5 minutes from a single host then drops 
# incomming connections from that host. Beyond a burst of 100 connections we 
# log at up 1 attempt per second to prevent filling of logs.
-N SSHBRUTE
-A SSHBRUTE -m recent --name SSH --set
-A SSHBRUTE -m recent --name SSH --update --seconds 300 --hitcount 10 -m limit --limit 1/second --limit-burst 100 -j LOG --log-prefix "iptables[SSH-brute]: "
-A SSHBRUTE -m recent --name SSH --update --seconds 300 --hitcount 10 -j DROP
-A SSHBRUTE -j ACCEPT

# Chain for preventing ping flooding - up to 6 pings per second from a single 
# source, again with log limiting. Also prevents us from ICMP REPLY flooding 
# some victim when replying to ICMP ECHO from a spoofed source.
-N ICMPFLOOD
-A ICMPFLOOD -m recent --set --name ICMP --rsource
-A ICMPFLOOD -m recent --update --seconds 1 --hitcount 6 --name ICMP --rsource --rttl -m limit --limit 1/sec --limit-burst 1 -j LOG --log-prefix "iptables[ICMP-flood]: "
-A ICMPFLOOD -m recent --update --seconds 1 --hitcount 6 --name ICMP --rsource --rttl -j DROP
-A ICMPFLOOD -j ACCEPT


###############################################################################
# 2. HOST SPECIFIC RULES                                                      #
#                                                                             #
# This section is a good place to enable your host-specific services.         #
# ! DO NOT FORGOT TO COPY THESE RULES TO firewall.ip6tables TO ALLOW IPV6 !   #
###############################################################################

# Accept HTTP and HTTPS
#-A INPUT -p tcp -m multiport --dports 80,443 --syn -m conntrack --ctstate NEW -j ACCEPT


###############################################################################
# 3. GENERAL RULES                                                            #
#                                                                             #
# This section contains general rules that should be suitable for most hosts. #
###############################################################################

# Accept worldwide access to SSH and use SSHBRUTE chain for preventing 
# brute-force attacks.
-A INPUT -p tcp --dport 22 --syn -m conntrack --ctstate NEW -j SSHBRUTE

# Permit useful IMCP packet types.
# Note: RFC 792 states that all hosts MUST respond to ICMP ECHO requests.
# Blocking these can make diagnosing of even simple faults much more tricky.
# Real security lies in locking down and hardening all services, not by hiding.
-A INPUT -p icmp --icmp-type 0  -m conntrack --ctstate NEW -j ACCEPT
-A INPUT -p icmp --icmp-type 3  -m conntrack --ctstate NEW -j ACCEPT
-A INPUT -p icmp --icmp-type 8  -m conntrack --ctstate NEW -j ICMPFLOOD
-A INPUT -p icmp --icmp-type 11 -m conntrack --ctstate NEW -j ACCEPT

# Do not log packets that are going to ports used by SMB 
# (Samba / Windows Sharing).
-A INPUT -p udp -m multiport --dports 135,445 -j DROP
-A INPUT -p udp --dport 137:139 -j DROP
-A INPUT -p udp --sport 137 --dport 1024:65535 -j DROP
-A INPUT -p tcp -m multiport --dports 135,139,445 -j DROP

# Do not log packets that are going to port used by UPnP protocol.
-A INPUT -p udp --dport 1900 -j DROP

# Do not log late replies from nameservers.
-A INPUT -p udp --sport 53 -j DROP

# Good practise is to explicately reject AUTH traffic so that it fails fast.
-A INPUT -p tcp --dport 113 --syn -m conntrack --ctstate NEW -j REJECT --reject-with tcp-reset

# Prevent DOS by filling log files.
-A INPUT -m limit --limit 1/second --limit-burst 100 -j LOG --log-prefix "iptables[DOS]: "

COMMIT


###############################################################################
# 4. HOST SPECIFIC NAT RULES                                                  #
#                                                                             #
# Uncomment this section if you want to use NAT table, e.g. for port          #
# forwarding, redirect, masquerade...                                         #
###############################################################################

#*nat

# Base policy
#:PREROUTING ACCEPT [0:0]
#:POSTROUTING ACCEPT [0:0]
#:OUTPUT ACCEPT [0:0]

# Redirect port 21 to local port 2121
#-A PREROUTING -i eth0 -p tcp --dport 21 -j REDIRECT --to-port 2121

# Forward port 8080 to port 80 on host 192.168.1.10
#-A PREROUTING -i eth0 -p tcp --dport 8080 -j DNAT --to-destination 192.168.1.10:80

#COMMIT