Provided by: sshguard_1.7.1-1_amd64 
NAME
sshguard - block brute-force attacks by aggregating system logs
SYNOPSIS
sshguard [-v] [-a thresh] [-b thresh:file] [-f service:pidfile] [-i pidfile] [-l source] [-p interval]
[-s interval] [-w address | file]
DESCRIPTION
sshguard protects hosts from brute-force attacks against SSH and other services. It aggregates system
logs and blocks repeat offenders using one of several firewall backends, including iptables, ipfw, and
pf.
sshguard can read log messages from standard input (suitable for piping from syslog) or monitor one or
more log files. Log messages are parsed, line-by-line, for recognized patterns. If an attack, such as
several login failures within a few seconds, is detected, the offending IP is blocked. Offenders are
unblocked after a set interval, but can be semi-permanently banned using the blacklist option.
See http://www.sshguard.net/docs/setup/ for setup instructions.
Other features, attack signatures, and additional documentation can be found at http://www.sshguard.net/.
OPTIONS
-a thresh (default 30)
Block an attacker when its dangerousness exceeds thresh. Each attack pattern that is matched
contributes a fixed dangerousness of 10.
-b thresh:file
Blacklist an attacker when its dangerousness exceeds thresh. Blacklisted addresses are added to
file so they can be read at the next startup. Blacklisted addresses are never automatically
unblocked, but it is good practice to periodically clean out stale blacklist entries.
-f service:pidfile
Deprecated. See LOG VALIDATION below.
-i pidfile
Write the PID of sshguard to pidfile.
-l source
Monitor source for log messages. By default, sshguard reads log messages from standard input. Give
this option once for every source to monitor instead. sshguard transparently handles log
rotations. When using this option, standard input is ignored, but can be re-added by giving '-l
-'.
-p interval (default 120 secs, or 2 minutes)
Wait at least interval seconds before releasing a blocked address. Repeat attackers are blocked
for 1.5 times longer after each attack. Because sshguard unblocks attackers only at infrequent
intervals, this parameter is inexact (actual blocks will be longer).
-s interval (default 1800 secs, or 30 minutes)
Forget about an attacker interval seconds after its last attempt. Its dangerousness will be reset
to zero.
-w address | file
Whitelist the given address, hostname, or address block. Alternatively, read whitelist entires
from file. This option can be given multiple times. See WHITELISTING below for details.
-v Print version information and exit.
ENVIRONMENT
SSHGUARD_DEBUG
Enable additional debugging information.
WHITELISTING
sshguard supports address whitelisting. Whitelisted addresses are not blocked even if they appear to
generate attacks. This is useful for protecting lame LAN users (or external friendly users) from being
incidentally blocked.
Whitelist addresses are controlled through the -w command-line option. This option can add explicit
addresses, host names and address blocks:
addresses
specify the numeric IPv4 or IPv6 address directly, like:
-w 192.168.1.10
or in multiple occurrences:
-w 192.168.1.10 -w 2001:0db8:85a3:0000:0000:8a2e:0370:7334
host names
specify the host name directly, like:
-w friendhost.enterprise.com
or in multiple occurrences:
-w friendhost.enterprise.com -w friend2.enterprise.com
All IPv4 and IPv6 addresses that the host resolves to are whitelisted. Hosts are resolved to
addresses once, when sshguard starts up.
address blocks
specify the IPv4 or IPv6 address block in the usual CIDR notation:
-w 2002:836b:4179::836b:0000/126
or in multiple occurrences:
-w 192.168.0.0/24 -w 1.2.3.128/26
file When longer lists are needed for whitelisting, they can be wrapped into a plain text file, one
address/hostname/block per line, with the same syntax given above.
sshguard can take whitelists from files when the -w option argument begins with a '.' (dot) or '/'
(slash).
This is a sample whitelist file (say /etc/friends):
# comment line (a '#' as very first character)
# a single IPv4 and IPv6 address
1.2.3.4
2001:0db8:85a3:08d3:1319:8a2e:0370:7344
# address blocks in CIDR notation
127.0.0.0/8
10.11.128.0/17
192.168.0.0/24
2002:836b:4179::836b:0000/126
# hostnames
rome-fw.enterprise.com
hosts.friends.com
And this is how sshguard is told to make a whitelist up from the /etc/friends file:
sshguard -w /etc/friends
The -w option can be used only once for files. For addresses, host names and address blocks it can be
used with any multiplicity, even with mixes of them.
LOG VALIDATION
Syslog and syslog-ng typically insert a PID of the generating process in every log message. This can be
checked for authenticating the source of the message and avoid false attacks to be detected because
malicious local users inject crafted log messages. This way sshguard can be safely used even on hosts
where this assumption does not hold.
Log validation is only needed when sshguard is fed log messages from syslog or from syslog-ng. When a
process logs directly to a raw file and sshguard is configured for polling logs directly from it, you
only need to adjust the log file permissions so that only root can write on it.
For enabling log validation on a given service the -f option is used as follows:
-f 100:/var/run/sshd.pid
which associates the given pidfile to the ssh service (code 100). A list of well-known service codes is
available at http://www.sshguard.net/docs/reference/service-codes/.
The -f option can be used multiple times for associating different services with their pidfile:
sshguard -f 100:/var/run/sshd.pid -f 123:/var/run/mydaemon.pid
Services that are not configured for log validation follow a default-allow policy (all of their log
messages are accepted by default).
PIDs are checked with the following policy:
1. the logging service is searched in the list of services configured for validation. If not found, the
entry is accepted.
2. the logged PID is compared with the pidfile. If it matches, the entry is accepted
3. the PID is checked for being a direct child of the authoritative process. If it is, the entry is
accepted.
4. the entry is ignored.
Low I/O load is committed to the operating system because of an internal caching mechanism. Changes in
the pidfile value are handled transparently.
SEE ALSO
syslog(1), syslog.conf(5), hosts_access(5)
Glossary: http://www.sshguard.net/docs/terminology/
Website: http://www.sshguard.net/
AUTHORS
Michele Mazzucchi <mij@bitchx.it>, Kevin Zheng <kevinz5000@gmail.com>