Ampere

An active network filter for Asterisk PBX

Synopsis

The application subscribes to Asterisk's Management Interface (AMI) security events. There is a table of penalties for each host. In case of any suspicious activity, the penalty raises, increment depends on event status. Legal event (such as successful auth) removes penalties. If the penalties are too high, host blocked in configured chain via iptables syscall. Each violator is stored in internal database. The chain is flushed once application starts, and previously stored rules applies back again.

Dependencies:

• Asterisk 12 or above
• Berkeley v5.x Database Libraries
• libpcre3
• iptables

Building

make - build stripped executable
make dev - build unstripped executable with debug symbols and some extra verbosity (such as parsed config variables, recived messages, etc)

Installation

• Put ampere.cfg into /etc/ampere/
• Put executable anywhere you want, e.g. /usr/lib/ampere/

Ampere is not acting like a natural UNIX daemon (for now) and should be forked via SystemD / SysV init script.

Example of ampere.service for systemd:

[Unit]
Description=Ampere
After=asterisk.service
Wants=asterisk.service

[Service]
Type=simple
TimeoutSec=120

SyslogIdentifier=ampere

ExecStart=/usr/lib/ampere/ampere -o /var/log/ampere.log

[Install]
WantedBy=multi-user.target

Configuring

Firewall

When the application starts, chain should exist; jumping into a chain should be configured.

Example of iptables -S output:

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-N ampere-firewall
-A INPUT -i eth0 -p udp -m udp --dport 5060 -j ampere-firewall
-A INPUT -i eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -j DROP

Config file

By default, the application reads config from /etc/ampere/ampere.cfg

The options and their defaults are:
host = 127.0.0.1 - AMI interface address. Due to iptables executes locally, it makes sense to only use loopback addresses
port = 5038 - AMI interface port
user = ampere - AMI interface login
pass = ampere - AMI interface secret
loyalty = 3 - Multiplier for penalties upper limit. In most cases than mean number of allowed authentication attempts
chain = ampere - name of chain in firewall table
trust = 0.0.0.0/32 - network address(/mask) of trusted host or network. It is possible to specify up to 16 params

Example of ampere.cfg:

pass = 123
loyalty = 4
chain = ampere-firewall
trust = 192.168.0.0/24
trust = 10.10.32.0/19

Database

Ampere creates an internal BerkleyDB database file at compile-time configured path. Directory should exist.

Logging

Ampere prints data to stdout/stderr. In a case of systemd daemonising, this output grabs by syslog.

Command-line

Valid options:
-h, --help Show this help
-V, --version Display version number
-a, --add Insert database entries, read one per line from STDIN
-l, --list List database entries
-d, --del Remove database entries, read one per line from STDIN
-c <config> Use alternative configuration file
-o <logfile> Set output stream to a file

Asterisk Management Interface

AMI also should be configured to accept connections and send security- and system-level events. Sending only those messages for which the application waits can be the useful. It can be done by specifying some eventfilter directives.

Example of asterisk's manager.conf

[general]
enabled = yes
webenabled = no
port = 5038
bindaddr = 127.0.0.1

[ampere]
secret = 123
read = security,system
write = no
eventfilter = Event: ChallengeResponseFailed
eventfilter = Event: ChallengeSent
eventfilter = Event: FailedACL
eventfilter = Event: InvalidPassword
eventfilter = Event: Shutdown
eventfilter = Event: SuccessfulAuth

Then reload asterisk:
asterisk -x "manager reload"

Stability

Ampere has tested and successfuly applied to production.

Prerequisites are:

• Asterisk 12.8.2 and 13.13.1
• OS Debian 8 with kernel 3.16.0-4-amd64
• GCC version 4.9.2