sshguard

block brute-force attacks by aggregating system logs

Date: March 16, 2021
Manual group:SSHGuard Manual
Manual section:8
Version: 2.4

SYNOPSIS

sshguard [-hv] [-a threshold] [-b threshold:blacklist_file] [-i pidfile] [-p blocktime] [-s detection_time] [-w address | whitelist_file] [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.

sshguard can monitor log files and the standard output of running a shell command. Log messages are parsed line-by-line for recognized attack patterns. Attackers are blocked when enough attack patterns are detected in a configurable time interval. Attackers are blocked temporarily but can also be permanently blocked using the blacklist option.

sshguard must be configured before its first run. See sshguard-setup(7).

OPTIONS

-a threshold (default 30)
Each detected attack increases an attacker's attack score, usually by 10. Block attackers when their attack score exceeds threshold.
-b threshold:blacklist_file
Blacklist an attacker when its attack score exceeds threshold. Blacklisted addresses are written to blacklist-file and never unblocked, even after restarting sshguard.
-i pidfile
Write the PID of sshguard to pidfile. pidfile is removed when sshguard exits.
-p blocktime (default 120)
Block first-time attackers for blocktime seconds. Subsequent blocks increase in duration by a factor of 1.5. Since sshguard unblocks attackers at random intervals, actual block times may be somewhat longer.
-s detection_time (default 1800)
Reset an attacker's attack score after detection_time seconds since the last attack. This means that attackers who attack every detection_time seconds are never blocked by sshguard. However, an increased detection_time may have an impact on legitimate users.
[-w address | whitelist_file]
Whitelist a single address, hostname, or address block given as address. This option can be given multiple times. Alternatively, provide an absolute path to a whitelist_file containing addresses to whitelist. See WHITELISTING.
-h
Print usage information and exit.
-v
Print version information and exit.

ENVIRONMENT

SSHGUARD_DEBUG
Set to enable verbose output from sshg-blocker.

FILES

%PREFIX%/etc/sshguard.conf
See sample configuration file.

WHITELISTING

Whitelisted addresses are never blocked. Addresses can be specified on the command line or be stored in a file.

On the command line, give the -w option one or more times with an IP address, CIDR address block, or hostname as an argument. Hostnames are resolved once at startup. If a hostname resolves to multiple addresses, all of them are whitelisted. For example:

sshguard -w 192.168.1.10 -w 192.168.0.0/24 -w friend.example.com
    -w 2001:0db8:85a3:0000:0000:8a2e:0370:7334
    -w 2002:836b:4179::836b:0000/126

If the argument to -w begins with a forward slash ('/') or dot ('.'), the argument is treated as the path to a whitelist file.

The whitelist file contains comments (lines beginning with '#'), addresses, address blocks, or hostnames, one per line.

SEE ALSO

sshguard-setup(7)