blacklist-scripts

This is a collection of shell scripts that are intended to block Linux systems and OpenWRT routers from known sources of malicious traffic. These scripts use iptables with highly efficient ipset module to check incoming traffic against blacklists populated from publicly available sources.

Emerging Threats provides similar rules that essentially run iptables for each blacklisted IP which is extremely inefficient in case of large blacklists. Using ipset means using just one iptables rule to perform a very efficient lookup in hash structure created by ipset.

Note: This script is a quick hack suitable primarily for embedded devices (OpenWRT, LEDE) rather than a complete solution for server. For the latter, have a look at FireHOL and its excellent FireHOL IP Lists add-on. Have a look at the FireHOL section further down.

Available blacklists

If you decide to use this script, these are the blacklists available by default:

• Emerging Threats - list of other known threats (botnet C&C, compromised servers etc) compiled from various sources, including Spamhaus DROP, Shadoserver and DShield Top Attackers
• www.blocklist.de - list of known password bruteforcers supplied by a network of fail2ban users
• iBlocklist - various free and subscription based lists
• Bogons - IP subnets that should never appear on public Internet; this includes RFC 1918 networks so running this on a machine in a private network will effectively shut its networking down

By default the script will only load Emerging Threats and Blocklist.de collections. Others may be added by simply appending to the URLS variable in the beginning of the script:

URLS="http://rules.emergingthreats.net/fwrules/emerging-Block-IPs.txt"
URLS="$URLS https://www.blocklist.de/downloads/export-ips_all.txt"

The script ignores empty lines or comments and will only extract anything that looks like an IP address (a.b.c.d) or CIDR subnet (a.b.c.d/nn). Each blacklist is loaded into a separate ipset collection so that logging unambigously identifies which blacklist blocked a packet.

The script also creates an empty manual-blacklist set that can be used by the administrator for manual blacklisting. For example:

ipset add manual-blacklist 217.146.93.122

Removal:

ipset delete manual-blacklist 217.146.93.122

OpenWRT

The script automatically detects OpenWRT environment (looking for uci) and will try to obtain the WAN interface name. The filtering will be then limited to WAN interface only.

Requirements:

• opkg install ipset curl

Installation:

cp blacklist.sh /etc/firewall.user
echo "01 01 * * * sh /etc/firewall.user" >>/etc/crontabs/root

The blacklist will be updated on daily basis.

Manual run:

sh /etc/firewall.user

LEDE

On LEDE the firewall comes up before network interfaces are configured so a service file is required to bring the blacklist when network is available. Create /etc/init.d/blacklist with the following contents and chmod a+x /etc/init.d/blacklist:

#!/bin/sh /etc/rc.common
START=30
COMMAND="sh /etc/firewall.user"
boot() {
   $COMMAND
}

Linux

Requirements:

• On Debian, Ubuntu and other apt systems: apt-get install ipset curl
• On RedHat, Fedora, CentOS and other RPM systems: yum install ipset curl

Installation:

cp blacklist.sh /etc/cron.daily/blacklist

The blacklist will be updated on daily basis.

Manual run:

sh /etc/cron.daily/blacklist

Integration with OSSEC

OSSEC HIDS is a host-intrusion detection engine for Unix and Windows servers. Its active response feature allows running a script in response to configured events, for example blocking an IP address detected as attempting to continuously bruteforce a SSH password.

The ipset-drop.sh is active response script to add offending IP addresses to a manual-blacklist set also created by the blacklist.sh script.

Installation:

cp ipset-drop.sh /var/ossec/active-response/bin

Example OSSEC configuration:

<command>
  <name>ipset-drop</name>
  <executable>ipset-drop.sh</executable>
  <expect>srcip</expect>
  <timeout_allowed>yes</timeout_allowed>
</command>

<active-response>
  <command>ipset-drop</command>
  <location>local</location>
  <rules_id>5720</rules_id> <!-- Rule: 5720 fired (level 10) -> Multiple SSHD authentication failures. -->
</active-response>

Another script router-drop.sh will perform the same action on a remote router over SSH. This is useful in case of embedded routers where OSSEC agent installation is unfeasibile. OpenWRT logs (over syslog) to a more powerful Linux box with OSSEC installed. On alerts the active response script installed that blocks uoffending IP addresses on the router:

  +---------+ ----- syslog -------> +-------+
--| OpenWRT |                       | Linux |
  |         |                       | OSSEC |
  +---------+ <- active response -- +-------+

The router-drop.sh script requires two configuration steps:

• configure the ROUTER variable to a SSH string for root login to the router (e.g. root@gw.example.com)
• install SSH keys to actually log in; the keys need to be installed on root account as this is where active response script are running

Example configuration:

 <command>
   <name>router-drop</name>
   <executable>router-drop.sh</executable>
   <expect>srcip</expect>
   <timeout_allowed>no</timeout_allowed>
 </command>

 <active-response>
   <command>router-drop</command>
   <location>local</location>
   <rules_id>51004</rules_id>
 </active-response>

Event 51004 is defined in /var/ossec/rules/dropbear_rules.xml and triggered by a series of unsuccessful password logins. Don't forget to add your trusted networks to <white_list> entries to prevent locking yourself out!

Samples

Number of blacklisted IP addresses:

# ipset list | wc -l
26160

Traffic (ICMP and TCP) from blacklisted IP addresses in router logs (OpenWRT):

# dmesg|grep BLOCK
[745433.590000] BLOCK emerging-Block-IPs.txt IN=eth0.2 OUT=br-lan MAC=64:70:12:c2:64:70:02:cc:24:73:9c:97:26:50:b9:10:08:00 SRC=217.146.93.122 DST=10.10.10.20 LEN=28 TOS=0x00 PREC=0x00 TTL=56 ID=54090 PROTO=ICMP TYPE=0 CODE=0 ID=48891 SEQ=0 MARK=0x10 
[745433.620000] BLOCK emerging-Block-IPs.txt IN=eth0.2 OUT=br-lan MAC=64:70:12:c2:64:70:02:cc:24:73:9c:97:26:50:b9:10:08:00 SRC=144.76.71.210 DST=10.10.10.20 LEN=28 TOS=0x00 PREC=0x40 TTL=51 ID=17805 PROTO=ICMP TYPE=0 CODE=0 ID=28814 SEQ=0 MARK=0x10 
[745484.510000] BLOCK emerging-Block-IPs.txt IN=eth0.2 OUT=br-lan MAC=64:70:12:c2:64:70:02:cc:24:73:9c:97:26:50:b9:10:08:00 SRC=69.194.235.103 DST=10.10.10.20 LEN=44 TOS=0x00 PREC=0x00 TTL=45 ID=0 DF PROTO=TCP SPT=443 DPT=58827 WINDOW=5840 RES=0x00 ACK SYN URGP=0 MARK=0x33

Traffic (SSH bruteforce scanners) from blacklisted IP addresses in web server logs (CentOS):

BLOCK export-ips_all.txt IN=eth1 OUT= MAC=bc:16:2e:08:69:d4:3c:08:f6:d9:93:a5:08:00 SRC=122.225.97.79 DST=10.179.134.230 LEN=40 TOS=0x00 PREC=0x00 TTL=101 ID=256 PROTO=TCP SPT=6000 DPT=22 WINDOW=16384 RES=0x00 SYN URGP=0 
BLOCK export-ips_all.txt IN=eth1 OUT= MAC=bc:16:2e:08:69:d4:3c:08:f6:d9:93:a5:08:00 SRC=61.174.51.207 DST=10.179.134.230 LEN=40 TOS=0x00 PREC=0x00 TTL=102 ID=256 PROTO=TCP SPT=6000 DPT=22 WINDOW=16384 RES=0x00 SYN URGP=0

Traffic (SSH password bruteforce scanners) blocked by OSSEC HIDS (Linux):

BLOCK manual-blacklist IN=eth1 OUT= MAC=bc:76:2e:08:69:d4:3c:08:f6:d9:93:a5:08:00 SRC=89.46.14.48 DST=10.179.134.230 LEN=60 TOS=0x00 PREC=0x00 TTL=48 ID=62214 DF PROTO=TCP SPT=51436 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 
BLOCK manual-blacklist IN=eth1 OUT= MAC=bc:76:2e:08:69:d4:3c:08:f6:d9:93:a5:08:00 SRC=89.46.14.48 DST=10.179.134.230 LEN=60 TOS=0x00 PREC=0x00 TTL=48 ID=62215 DF PROTO=TCP SPT=51436 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 

FireHOL Blacklists

If you are looking for a mature firewall management solution for Linux that supports blacklists, definitely have a look at FireHOL and its excellent FireHOL IP Lists add-on. Compared to FireHOL, this script is a quick hack and I keep maintaining it primarily because FireHOL seems to be an overkill for OpenWRT/LEDE devices.

Quick start with FireHOL blacklists:

• Run update-ipsets enable dshield and then update-ipsets
• Modify /etc/firehol/firehol.conf (remember to run firehol start afterwards)

ipv4 ipset create dshield hash:net
ipv4 ipset addfile dshield ipsets/dshield.netset
blacklist4 stateful inface eth0 connlog "BLACKLIST " ipset:dshield
interface eth0 world4
    server4 ssh deny src4 ipset:manual-blacklist
    ...