xref: /dragonfly/usr.sbin/sshlockout/sshlockout.8 (revision cdb47f1a)

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.\" This code is derived from software contributed to The DragonFly Project
.\" by Matthew Dillon <dillon@backplane.com>
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.Dd September 13, 2017
.Dt SSHLOCKOUT 8
.Os
.Sh NAME
.Nm sshlockout
.Nd utility to block port 22 on preauth failures
.Sh SYNOPSIS
.Bd -literal
#
# pf(4) configuration.
#

# in /etc/pf.conf
#
table <lockout> persist { }

# and later in /etc/pf.conf - see below
#
block in quick on $ext_if proto tcp from <lockout> to any port 22

# in /etc/syslog.conf
#
auth.info;authpriv.info          |exec /usr/sbin/sshlockout -pf "lockout"

# in root's crontab
#
3 3 * * *       pfctl -tlockout -T expire 86400

#
# ipfw(8) configuration.
#
ipfw table 0 create
ipfw add deny ip from '<0>' to any

# in /etc/syslog.conf
#
auth.info;authpriv.info         |exec /usr/sbin/sshlockout -ipfwtbl 0

# in root's crontab
#
3 3 * * *       ipfw -fq table 0 expire 86400
.Ed
.Sh DESCRIPTION
This program is generally installed in
.Pa /etc/syslog.conf
as a pipe to parse the
.Xr sshd 8
demons error log in realtime.
In addition, a root crontab entry should generally be created to clean
out stale entries in the
.Xr pf 4
or
.Xr ipfw 8
.Ar table
at least once a day.
Using expire instead of flush will maintain a rolling window of locked out
IPs.
The
.Xr pf 4
or
.Xr ipfw 8
module must be loaded and running with the table and rules properly
configured.
.Pp
This program will monitor the ssh syslog output and keep track of attempts
to login to unknown users as well as preauth failures.
If 5 attempts fail in any one hour period, a permanent entry is added to the
.Xr pf 4
or
.Xr ipfw 8
.Ar table
for the associated IP address.
You still have to add a rule to
.Xr pf.conf 5
or use
.Xr ipfw 8
to block IP addresses listed in this table.
The cron entry you create cleans the block list out typically once a day.
.Pp
This program generally limits brute-force attempts to break into a machine
via ssh.
.Pp
When setting up the
.Xr pf 4
or
.Xr ipfw 8
rules,
note that the table will be filled based on failed ssh connections destined
to that particular machine.
If the machine is acting as a router you can decide whether you want the
.Xr pf 4
or
.Xr ipfw 8
rule to lockout that suspect IP to just the machine,
or to everything it routes to.
We usually recommend an unconditional blocking rule.
.Sh NOTICE
This program is still a work in progress.
.Sh SEE ALSO
.Xr ssh 1 ,
.Xr pf 4 ,
.Xr syslog.conf 5 ,
.Xr ipfw 8 ,
.Xr sshd 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Dx 4.1 .
.Sh AUTHORS
.An Matthew Dillon Aq Mt dillon@backplane.com