NAME

bruteblock —

utility to block bruteforce attacks

SYNOPSIS

bruteblock [-f configfile] [-h]

bruteblockd -t table [-s sleep] [-p pidfile] [-f] [-h]

DESCRIPTION

Bruteblock allows system administrators to block various bruteforce attacks on UNIX services. The program analyzes system logs and adds attacker's IP address into ipfw2 table effectively blocking them. Addresses are automatically removed from the table after specified amount of time. Bruteblock uses regular expressions to parse logs, which provides flexibility allowing it to be used with almost any network service. Bruteblock is written in pure C, doesn't use any external programs and work with ipfw2 tables via raw sockets API.

Bruteblock consists of two binaries: bruteblock and bruteblockd.

bruteblock

bruteblock is intended to be used in /etc/syslog.conf to pipe logs into. It does log analysis and adds attacker IP's into ipfw2 table. Along with address and mask, every entry in ipfw2 table has value field, which is used by bruteblock to store expiration time as 32 bit UNIX timestamp.

The following command line options are available for bruteblock:

-f configfile: Specify path to config file
-h: Display help

bruteblockd

bruteblock is a daemon, which checks ipfw2 table periodically and removes expired entries.

The following command line options are available for bruteblockd:

-t table: Specify numer of ipfw2 table
-s sleep: Specify table check interval
-p pidfile: Specify location of the pid file
-f: Run the daemon in the foreground (do not daemonize)
-h: Display help

Such design allows to avoid any IPC use and to store entries for different services in one table. Also makes it is easy for the administrator to get list of currently blocked addresses and edit the list if needed so.

CONFIGURATION FILE

Configuration file for bruteblock utility allows you to set following values:

regexp: regular expression in perl-compatible format that is used to extract failed password attempts from log files.
max_count, within_time: defines time interval and maximum number of failed password attempts during that interval. If the number is exceeded by specific IP, that IP is blocked.
reset_ip: time-to-live of table entry. When it expires, address is removed from the table, thus being unblocked.
ipfw2_table_no: number of ipfw2 table to add bad IPs to. Must match -t parameter of bruteblockd.

EXAMPLE (SSH)

First, you need to establish log processing to determine attacker's IPs and add them to ipfw2 table. Edit /etc/syslog.conf and add the following entry:

auth.info;authpriv.info	| exec /usr/local/sbin/bruteblock -f /usr/local/etc/bruteblock/ssh.conf

then restart syslogd.

Next, you'll want to setup periodical cleanup of ipfw2 table. Add following lines to /etc/rc.conf:

bruteblockd_enable="YES"
bruteblockd_table="1"
bruteblockd_flags="-s 5"

don't forget to change table number and sleep interval to match your needs.

Now launch bruteblockd: /usr/local/etc/rc.d/bruteblockd.sh start

Finally, setup your ipfw to block addresses contained in the table:

ipfw add 100 deny ip from me to table\(1\)
ipfw add 100 deny ip from table\(1\) to me

you may want to add these lines to you /etc/rc.firewall.

SYSTEM REQUIREMENTS

Bruteblock requires FreeBSD 5.3 and above (tested on FreeBSD 5.3, 5.4, 6.1) with ipfw2 firewall.

AUTHOR

Alex Samorukov ⟨samm@os2.kiev.ua⟩, http://samm.kiev.ua/bruteblock/