Free filtering software for linux

Packet filtering setup script by Anthony C. Zboralski. Adapted by Didi Damian for iptables version 1.0.0

Sample:

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# Set up variables
EXT_IF="eth0"
INT_IF="eth1"
EXT_IP=24.x.x.x/32
INT_IP=192.168.0.1/32
EXT_NET=24.x.x.0/24
INT_NET=192.168.0.0/24
MASQ_NETS="192.168.0.0/24"
LOCAL_ADDRS="127.0.0.0/8 192.168.0.1/32 24.x.x.x/32"
MAIL_RELAY=24.x.x.x/32
SMB_ACCESS="192.168.0.2/32"
SMB_BCAST="192.168.0.255/32"

# Turn on IP forwarding
echo Turning on IP forwarding.
echo 1 > /proc/sys/net/ipv4/ip_forward

# Load the ip_tables module
echo Loading ip_tables module.
/sbin/modprobe ip_tables || exit 1
# I let the kernel dynamically load the other modules

echo Flush standard tables.
iptables --flush INPUT
iptables --flush OUTPUT
iptables --flush FORWARD
echo Deny everything until firewall setup is completed.
iptables --policy INPUT DROP
iptables --policy OUTPUT DROP
iptables --policy FORWARD DROP

CHAINS=`iptables -n -L |perl -n -e /Chains+(S+)/ && !($1 =~ /^(INPUT|FORWARD|OUTPUT)$/) && print "$1 "`
echo Remove remaining chains:
echo $CHAINS
for chain in $CHAINS; do
iptables --flush $chain
done
# 2nd step cause of dependencies
for chain in $CHAINS; do
iptables --delete-chain $chain
done

for net in $MASQ_NETS; do
# I delete all the rules so you can rerun the scripts without bloating
# your nat entries.
iptables -D POSTROUTING -t nat -s $MASQ_NETS -j MASQUERADE 2>/dev/null
iptables -A POSTROUTING -t nat -s $MASQ_NETS -j MASQUERADE || exit 1
done
iptables --policy FORWARD ACCEPT

# Create a target for logging and dropping packets
iptables --new LDROP 2>/dev/null
iptables -A LDROP --proto tcp -j LOG --log-level info
--log-prefix "TCP Drop "
iptables -A LDROP --proto udp -j LOG --log-level info
--log-prefix "UDP Drop "
iptables -A LDROP --proto icmp -j LOG --log-level info
--log-prefix "ICMP Drop "
iptables -A LDROP --proto gre -j LOG --log-level info
--log-prefix "GRE Drop "

iptables -A LDROP -f -j LOG --log-level emerg
--log-prefix "FRAG Drop "
iptables -A LDROP -j DROP

# Create a table for watching some accepting rules
iptables --new WATCH 2>/dev/null
iptables -A WATCH -m limit -j LOG --log-level warn --log-prefix "ACCEPT "
iptables -A WATCH -j ACCEPT


echo Special target for local addresses:
iptables --new LOCAL 2>/dev/null
echo $LOCAL_ADDRS
for ip in $LOCAL_ADDRS; do
iptables -A INPUT --dst $ip -j LOCAL
# iptables -A INPUT --src $ip -i ! lo -j LDROP # lame spoof protect
done
echo Authorize mail from mail relay.
iptables -A LOCAL --proto tcp --syn --src $MAIL_RELAY --dst $EXT_IP --dport 25 -j ACCEPT


echo Authorizing samba access to:
echo $SMB_ACCESS
iptables --new SMB 2>/dev/null
for ip in $SMB_ACCESS; do
iptables -A SMB -s $ip -j ACCEPT
done
iptables -A LOCAL --proto udp -i ! $EXT_IF --dport 135:139 -j SMB
iptables -A LOCAL --proto tcp -i ! $EXT_IF --dport 135:139 -j SMB
iptables -A LOCAL --proto tcp -i ! $EXT_IF --dport 445 -j SMB
iptables -A INPUT -i ! $EXT_IF --dst $SMB_BCAST -j ACCEPT #lame samba broadcast

echo Drop and log every other incoming tcp connection attempts.
iptables -A LOCAL -i ! lo --proto tcp --syn --j LDROP

echo Authorize dns access for local nets.
for net in $MASQ_NETS 127.0.0.0/8; do
iptables -A INPUT --proto udp --src $net --dport 53 -j ACCEPT
done


echo Enforcing up ICMP policies, use iptables -L ICMP to check.
# If you deny all ICMP messages you head for trouble since it would
# break lots of tcp/ip algorythm (acz)
iptables --new ICMP 2>/dev/null
iptables -A INPUT --proto icmp -j ICMP
iptables -A ICMP -p icmp --icmp-type echo-reply -j ACCEPT
iptables -A ICMP -p icmp --icmp-type destination-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type network-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type host-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type protocol-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type port-unreachable -j ACCEPT
iptables -A ICMP -p icmp --icmp-type fragmentation-needed -j LDROP
iptables -A ICMP -p icmp --icmp-type source-route-failed -j WATCH
iptables -A ICMP -p icmp --icmp-type network-unknown -j WATCH
iptables -A ICMP -p icmp --icmp-type host-unknown -j WATCH
iptables -A ICMP -p icmp --icmp-type network-prohibited -j WATCH
iptables -A ICMP -p icmp --icmp-type host-prohibited -j WATCH
iptables -A ICMP -p icmp --icmp-type TOS-network-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type TOS-host-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type communication-prohibited -j WATCH
iptables -A ICMP -p icmp --icmp-type host-precedence-violation -j LDROP
iptables -A ICMP -p icmp --icmp-type precedence-cutoff -j LDROP
iptables -A ICMP -p icmp --icmp-type source-quench -j LDROP
iptables -A ICMP -p icmp --icmp-type redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type network-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type host-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type TOS-network-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type TOS-host-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type echo-request -j WATCH
iptables -A ICMP -p icmp --icmp-type router-advertisement -j LDROP
iptables -A ICMP -p icmp --icmp-type router-solicitation -j LDROP
iptables -A ICMP -p icmp --icmp-type time-exceeded -j WATCH
iptables -A ICMP -p icmp --icmp-type ttl-zero-during-transit -j WATCH
iptables -A ICMP -p icmp --icmp-type ttl-zero-during-reassembly -j WATCH
iptables -A ICMP -p icmp --icmp-type parameter-problem -j WATCH
iptables -A ICMP -p icmp --icmp-type ip-header-bad -j WATCH
iptables -A ICMP -p icmp --icmp-type required-option-missing -j WATCH
iptables -A ICMP -p icmp --icmp-type timestamp-request -j LDROP
iptables -A ICMP -p icmp --icmp-type timestamp-reply -j LDROP
iptables -A ICMP -p icmp --icmp-type address-mask-request -j LDROP
iptables -A ICMP -p icmp --icmp-type address-mask-reply -j LDROP
iptables -A ICMP -p icmp -j LDROP

echo Authorize tcp traffic.
iptables -A INPUT --proto tcp -j ACCEPT

echo Authorize packet output.
iptables --policy OUTPUT ACCEPT

#echo reject ident if you drop em you gotta wait for timeout
#iptables -I LOCAL --proto tcp --syn --dst $EXT_IP --dport 113 -j REJECT

echo Drop and log all udp below 1024.
iptables -A INPUT -i ! lo --proto udp --dport :1023 -j LDROP

echo Drop rpc dynamic udp port:
RPC_UDP=`rpcinfo -p localhost|perl -n -e /.*udps+(d+)s+/ && print $1,"n"|sort -u`
echo $RPC_UDP
for port in $RPC_UDP; do
iptables -A LOCAL -i ! lo --proto udp --dport $port -j LDROP
done

echo Authorize udp above 1024.
iptables -A INPUT --proto udp --dport 1024: -j ACCEPT

POE::Filter::LZW::Progressive is a POE filter wrapped around Compress::LZW::Progressive.

Shrew Proxy/Filter is a tiny proxy built on WEBricks HTTPProxyServer, extended for both URL and content filtering. Shrew Proxy/Filter is designed to be small, simple to configure, and easy to install.

It is extremely small, lightweight, and works quite well. All blacklists (both URL and content) are plain text, so most published lists can be simply dropped in and used.

Filter::Simple::Compile is a drop-in replacement to Filter::Simple.

SYNOPSIS

Drop-in replacement for Filter::Simple:
package MyFilter;
use Filter::Simple::Compile;
FILTER { ... };

This way also works:
use Filter::Simple::Compile sub { ... };

This module lets you write Module::Compile extensions that are compatible with Filter::Simples API.

Additionally, no Filter::Simple::Compile does the same thing as use Filter::Simple::Compile, except the meaning for use and no will be reversed for your filter:

package MyFilter;
no Filter::Simple::Compile sub { ... }

# "no MyFilter" begins filtering
# "use MyFilter" terminates it

Compact Filter is a network packet filter for Linux. It features an easy-to-use compact filter representation and high performance.
The main features are: easy to use interface, compact filter representation (memory efficient), and very high performance.
A difference between CF and other firewalls, such as Netfilter, is its representation of the ruleset. In CF the user writes a filter which is then compiled and optimized in user-space. The optimized filter is then loaded into the kernel (using netlink). Consequently the in kernel packet filtering code only needs funtionality for setting up a filter and filtering packets, while the more complex code of optimizing the filter remains in user-space.
Because of the continuous increase of the bandwidth and the security threats, firewalls have to evolve towards more efficient filtering schemes. The truth is that the existing scheme does not scale so well with the combined growth of bandwidth and rulesets.
Our aim is to try another approach to perform packet filtering where we minimize the complexity of the filtering process. This result in, both, a reduction of the required CPU power to filter packets and a simpler (and smaller) kernel code. Of course, we are pushing all the smart and complex part out to the user-space, but, developing in user-space is much simpler and safer.
Enhancements:
- changed -d option to delete all filters
- added -D option to delete a specific filter
- changed default policy to permit rather than deny
- added -l option on flex to support --yylineno on older versions of flex
- new and improved install guide

slackware spam filter allows you to install spam filtering capabilities onto a slackware 9.1 box.

this is a very simple way to install spam filtering capabilities onto a slackware 9.1 box. its pretty simple: install.sh will install/upgrade a few packages in the packages/ directory. then itll patch the system and the installed packages to work together and filter that evil spam.

finally there are some scripts in the scripts/ directory which you can use to maintain your spam filter and stuff. when the system is patched there will also be a few new tools for you to use;

sa-learn-md-wrapper is used by the spam filter as an easy way to learn spam from inside a maildrop filter, and sa-rebuild is an easy tool to rebuild the bayesian filtering index for a couple of users or all of them at once.

run install.sh to install the packages and revised configuration for each
package.

run enable_mail_for_user.sh with users to add and the script will add users and enable them for use with the mail system.

run create_fetchmail_config.sh to create (or add onto) a fetchmail config file in a users home directory. then run fetchmail for that user if you intend on using fetchmail