Fail2Ban (with iptables) And Asterisk
Page Contents
Fail2Ban
Fail2Ban is a limited intrusion detection/prevention system. It works by scanning log files and then banning IPs based on the entries in those logs. Note that Digium is moving away from writing security information to log files, and is now using AMI events. Consider fail2ban a short-term solution only.
You can get Fail2Ban, as well as more documentation, at www.fail2ban.org. At the time this is being written, the current release is 0.8.4.
Fail2Ban With Asterisk
The following describes how to setup Fail2Ban to protect an Asterisk PBX from SIP brute force attempts and scans utilizing the iptables firewall.
SECURITY NOTE: fail2ban is rather limited in its ability to detect attacks against asterisk.
More info http://forums.asterisk.org/viewtopic.php?p=159984
Consider a more comprehensive product like the free edition of SecAst www.generationd.com
Easy Install Script for Fail2ban version 0.8.4 / Red Hat
This script was written by Cédric Brohée in order to simplify and accelerate the integration of the solution in a basic Asterisk configuration on Red Hat.
Do not hesitate to read the bash script and make changes to match your own configuration.
Before running it, you will have to do chmod 755.
Download script with new dedicated sources :
Installing
Log into the system and su – root, or sudo -i to get a root shell on Ubuntu.
CentOS/Red Hat (this method may install an older version of fail2ban):
Install rpmforge or optionally fetch the fail2ban rpm directly from rpmforge.
Install fail2ban using yum:
yum install fail2ban
Debian/Ubuntu:
apt-get install fail2ban
Source installation:
Change directories to /usr/src:
cd /usr/src
Download and extract Fail2Ban (check for newer releases):
wget http://sourceforge.net/projects/fail2ban/files/fail2ban-stable/fail2ban-0.8.4/fail2ban-0.8.4.tar.bz2/download
tar jxf fail2ban-0.8.4.tar.bz2
Enter the Fail2Ban directory you just extracted:
cd fail2ban-0.8.4
Make sure python and iptables are installed:
CentOS/Red Hat:
yum install python iptables
Debian/Ubuntu:
apt-get install python iptables
Install Fail2Ban:
python setup.py install
Install the Fail2Ban init script (for source installations):
Centos/Red Hat (if you installed via yum/rpm, the init script has already been installed):
cp /usr/src/fail2ban-0.8.4/files/redhat-initd /etc/init.d/fail2ban
chmod 755 /etc/init.d/fail2ban
For other distributions’ init scripts, please refer to documentation specific to them.
Configure Fail2Ban
We need to create a configuration for Fail2Ban so that it can understand attacks against Asterisk.
Create a new filter configuration for Asterisk:
touch /etc/fail2ban/filter.d/asterisk.conf
The contents of /etc/fail2ban/filter.d/asterisk.conf should be the following:
Generic (without using /var/log/asterisk/security)
# Fail2Ban configuration file
#
#
# $Revision: 250 $
#
[INCLUDES]
# Read common prefixes. If any customizations available -- read them from
# common.local
#before = common.conf
[Definition]
#_daemon = asterisk
# Option: failregex
# Notes.: regex to match the password failures messages in the logfile. The
# host must be matched by a group named "host". The tag "<HOST>" can
# be used for standard IP/hostname matching and is only an alias for
# (?:::f{4,6}:)?(?P<host>\S+)
# Values: TEXT
#
# Asterisk 1.4 use the following failregex
failregex = NOTICE.* .*: Registration from '.*' failed for '<HOST>' - Wrong password
NOTICE.* .*: Registration from '.*' failed for '<HOST>:.*' - No matching peer found
NOTICE.* .*: Registration from '.*' failed for '<HOST>' - No matching peer found
NOTICE.* .*: Registration from '.*' failed for '<HOST>' - Username/auth name mismatch
NOTICE.* .*: Registration from '.*' failed for '<HOST>' - Device does not match ACL
NOTICE.* .*: Registration from '.*' failed for '<HOST>' - Peer is not supposed to register
NOTICE.* .*: Registration from '.*' failed for '<HOST>' - ACL error (permit/deny)
NOTICE.* .*: Registration from '.*' failed for '<HOST>' - Device does not match ACL
NOTICE.* <HOST> failed to authenticate as '.*'$
NOTICE.* .*: No registration for peer '.*' \(from <HOST>\)
NOTICE.* .*: Host <HOST> failed MD5 authentication for '.*' (.*)
NOTICE.* .*: Failed to authenticate user .*@<HOST>.*
NOTICE.* .*: Sending fake auth rejection for device .*\<sip:.*\@<HOST>\>;tag=.*
# In Asterisk 1.8 use the same as above, but after <HOST> add :.* before the single quote. This is because in Asterisk 1.8, the log file includes a port number which 1.4 did not.
# Option: ignoreregex
# Notes.: regex to ignore. If this regex matches, the line is ignored.
# Values: TEXT
#
ignoreregex =
If you’re having issues with your system not banning properly when the “Registration from” section in your log file contains a quotation mark (“) as in this example:
[2011-04-07 17:53:11] NOTICE[7557] chan_sip.c: Registration from '"69106698"<sip:69106698@123.123.123.123>' failed for '123.123.123.123' - No matching peer found
Add the following line, with the others above, in asterisk.conf:
NOTICE.* .*: Registration from ‘\”.*\”.*’ failed for ‘<HOST>’ – No matching peer found
Recently noticed attacks:
[2011-06-21 17:53:11] NOTICE[7557] chan_sip.c: Registration from '"XXXXXXXXXX"<sip:XXXXXXXXXX@123.123.123.123>' failed for '123.123.123.123' - Wrong Password
Adding the following line will block these attempts:
NOTICE.* .*: Registration from ‘\”.*\”.*’ failed for ‘<HOST>’ – Wrong password
Using new /var/log/asterisk/security
For this you will need an Asterisk that comes with the new Asterisk Security Framework (Asterisk 10+). You will also need to enable the log output in logger.conf by adding or uncommenting the line “security => security”. Likewise, you willl also need to ensure the date format has been changed in logger.conf to “dateformat=%F %T”.
# Fail2Ban configuration file
#
#
# $Revision: 250 $
#
[INCLUDES]
# Read common prefixes. If any customizations available -- read them from
# common.local
#before = common.conf
[Definition]
#_daemon = asterisk
# Option: failregex
# Notes.: regex to match the password failures messages in the logfile. The
# host must be matched by a group named "host". The tag "<HOST>" can
# be used for standard IP/hostname matching and is only an alias for
# (?:::f{4,6}:)?(?P<host>\S+)
# Values: TEXT
#
failregex = SECURITY.* SecurityEvent="FailedACL".*RemoteAddress=".+?/.+?/<HOST>/.+?".*
SECURITY.* SecurityEvent="InvalidAccountID".*RemoteAddress=".+?/.+?/<HOST>/.+?".*
SECURITY.* SecurityEvent="ChallengeResponseFailed".*RemoteAddress=".+?/.+?/<HOST>/.+?".*
SECURITY.* SecurityEvent="InvalidPassword".*RemoteAddress=".+?/.+?/<HOST>/.+?".*
# Option: ignoreregex
# Notes.: regex to ignore. If this regex matches, the line is ignored.
# Values: TEXT
#
ignoreregex =
Next edit /etc/fail2ban/jail.conf to include the following section so that it uses the new filter. This does a 3-day ban on the IP that performed the attack. It is recommend to set the bantime in the [DEFAULT] section so if affects all attacks. It is also recommend to turn on an iptables ban for ssh, httpd/apache, and ftp if they are running on the system. Be sure to edit the sendmail-whois action to send notifications to an appropriate address:
Generic (without using /var/log/asterisk/security)
[asterisk-iptables]
enabled = true
filter = asterisk
action = iptables-allports[name=ASTERISK, protocol=all]
sendmail-whois[name=ASTERISK, dest=root, sender=fail2ban@example.org]
logpath = /var/log/asterisk/messages
maxretry = 5
bantime = 259200
note: logpath = /var/log/asterisk/messages is for vanilla asterisk, use logpath = /var/log/asterisk/full for freepbx. You can check the name of the log file in logger.conf.
note: if fail2ban still failed to identify login attempts, try the syslog logging way.
Using new /var/log/asterisk/security
[asterisk-iptables]
enabled = true
filter = asterisk
action = iptables-allports[name=ASTERISK, protocol=all]
sendmail-whois[name=ASTERISK, dest=root, sender=fail2ban@example.org]
logpath = /var/log/asterisk/security
maxretry = 5
bantime = 259200
Don’t Ban Yourself
We don’t want to ban ourselves by accident. Edit /etc/fail2ban/jail.conf and edit the ignoreip option under the [DEFAULT] section to include your IP addresses or network, as well as any other hosts or networks you do not wish to ban. Note that the addresses must be separated by a SPACE character!
Asterisk Logging
We must change how Asterisk does its time stamp for logging. The default format does not work with Fail2Ban because the pattern Fail2Ban uses that would match this format has a beginning of line character (^), and Asterisk puts its date/time inside of []. The other formats that Fail2Ban supports, however, do not have this character and can be used with Asterisk.
To change this format, open /etc/asterisk/logger.conf and add the following line under [general] section (You may have to create this before the [logfiles] section). This causes the date and time to be formatted as Year-Month-Day Hour:Minute:Second, [2008-10-01 13:40:04] is an example.
[general]
dateformat=%F %T
Then reload the logger module for Asterisk. At the command line, run the following command:
asterisk -rx “logger reload”
If for some reason you do not want to change the date/time format for your normal asterisk logs (maybe you already have scripts that use it or something and do not want to edit them), you can do the following instead:
In /etc/asterisk/logger.conf, add the following line under the [logfiles] section for Asterisk to log NOTICE level events to the syslog (/var/log/messages) as well as its normal log file. These entries in syslog will have a Date/Time stamp that is usable by Fail2Ban.
syslog.local0 => notice
Be sure to reload the logger module for Asterisk — check above for the command to do so. If you chose this option, you will also have to change the/etc/fail2ban/jail.conf setting under the [asterisk-iptables] section for the logpath option to the following:
logpath = /var/log/messages
Turning it On
Now it is time to put fail2ban to work. There are a couple steps we need to do first.
Turn IPTABLES on
By default, iptables allows all traffic. So if we turn it on, it will not block any traffic until Fail2Ban creates deny rules for attackers. You should create your own firewall rules and setup for iptables, but that is beyond the scope of this guide. Just know that Fail2Ban, by default, inserts rules at the top of the chain, so they will override any rules you have configured in iptables. This is good because you may allow all sip traffic in and then the Fail2Ban will block individual hosts, after they have done an attack, before they are allowed by this rule again.
To start iptables, run the following as root:
/etc/init.d/iptables start
Depending on your install, you may or may not have the iptables init script installed. Please refer to an iptables install/setup guide for your distribution for more information.
Turn on Fail2Ban
To start Fail2Ban, run the following as root:
/etc/init.d/fail2ban start
Check It
If both started properly, issue the following command to view your iptables rules:
iptables -L -v
You should see something like the following for the INPUT chain (you will see more if you have other Fail2Ban filters enabled):
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
2104K 414M fail2ban-ASTERISK all — any any anywhere anywhere
If you do not see something similar to that, then you have some troubleshooting to do; check out /var/log/fail2ban.log.
If you do not see all your rules, or if you see a different subset of rules after stopping and restarting fail2ban, you may be experiencing the issue described on this page on the Fail2ban talk:Community Portal and may wish to use the suggested fix:
fail2ban.action.action ERROR on startup/restart
I had multiple fail2ban.action.action ERROR on startup/restart. It seems there was a “race” condition with iptables. I solved the problem completely on my system by editing /usr/bin/fail2ban-client and adding a time.sleep(0.1)
def __processCmd(self, cmd, showRet = True):
beautifier = Beautifier()
for c in cmd:
time.sleep(0.1)
beautifier.setInputCmd(c)
Turn it on for good
If all is well up to this point, let’s make sure that fail2ban and iptables restart with the server by issuing the following commands.
Centos/Red Hat:
chkconfig iptables on
chkconfig fail2ban on
Debian/Ubuntu:
update-rc.d iptables defaults
update-rc.d fail2ban defaults
You should now be somewhat protected against SIP scans and brute force attacks!
Try a reboot
Once you have fail2ban working ok, make sure that it continues that way after rebooting the server. On some distributions (including Ubuntu daper) fail2ban won’t start after the system reboots because the /var/run/fail2ban directory gets deleted and needs to be re-created. This can be frustrating as there is also nothing that shows up in the logs to indicate what the problem is. If this happens, please see the link below for instructions on modifying the startup script so that it checks for and creates the /var/run/fail2ban directory if needed:
http://informationideas.com/news/2010/04/21/fail2ban-does-not-start-after-reboot/
Additional Information
- For more comprehensive intrusion detection/prevention look at SecAst www.generationd.com, which tracks dial cadence, call volumes per user/peer, geographic IP geographic location, etc. to ban users. The free edition alone does more than fail2ban. Check out wiki page SecAst (Asterisk Intrusion Detection and Prevention)
- For those who may want a bit of additional security, this thread on iptables rate limiting at the PBX in a Flash Forum discusses a possible way to limit the number of attempts a bot can make at registering before fail2ban kicks in (e.g., if the bot is so fast it can make many attempts before fail2ban detects that many > 3).
- You may also want to consider adding Asterisk security through geographic IP address restriction
- See http://www.opensolutions.ie/blog/2010/09/sip-brute-force-attacks/ for a quick howto on using Fail2ban with Ubuntu/Debian as well as some discussion on SIP brute force attacks.
- An alternative to fail2ban which is more simple (but of course less configurable). New version using Perl Net::Pcap. Unlike fail2ban, this tool does not peek into asterisk logs. http://www.dumaisnet.ca/index.php?article=35794ced17be93fdb1a28f73f754512c
- Alternate using Perl and iptables: Team Forrest – Automatically Block Failed SIP Peer Registrations
- You can also use the free VoIP Block List by itself or combined with fail2ban to protect your server. This is a list of hostile IP addresses you should consider proactively blocking – the IPs are gathered from various honey-pots and from other VoIP users who report hacking attempts on their systems to the list.
