sshutout periodically monitors log files looking for multiple failed login
attempts via the sshd (optionally, sshd2). It is meant to mitigate what
is commonly known as "dictionary attacks," i.e. scripted brute force
attacks that use lists of user IDs and passwords to effect unauthorized
intrusions. Typically such attacks fill up the system logs with hundreds
or even thousands of log entries for the failed login attempts. Aside
from the nuisance of wasted space, wasted bandwidth, and reduced signal
to noise ratio in the logs, the attacks can pose a real danger to
systems with weak ID and password combinations.

This package blunts such attacks by creating firewall rules to block
individual offenders from accessing the system. These rules are created
when an attack signature is detected, and after a configurable expiry
interval has elapsed, the rules are deleted.

While sshutout can help reduce the severity and impact of dictionary
attacks, it is by no means a substitute for a good password policy.
A password policy is the front line of defense against intrusion and
should be given careful consideration. sshutout is merely one small tool
intended to help reduce log clutter and diminish the incentive to mount
dictionary attacks.

• Michael Shigorin

• sshutout