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SSHGUARD-SETUP(7) SSHGuard Manual SSHGUARD-SETUP(7) NAME sshguard-setup - setting up SSHGuard on your system DESCRIPTION To set up SSHGuard, write sshguard.conf and set up the backend, if nec- essary. Configuration options are documented in the sample configura- tion file. A good starting point is to copy it and make the necessary changes: 1. Set BACKEND. You may also need to set it up to work with SSHGuard (see BACKENDS). 2. Set FILES, LOGREADER, or both. Alternatively, give sshguard a list of files to monitor as positional arguments on the command-line. Use FILES to specify a space-separated list of log files to monitor. Use LOGREADER to specify a shell command to run to obtain logs. Both settings are ignored if files are given on the command-line. Sample LOGREADER commands for journalctl(1) and macOS 10.12+ are avail- able in the sample configuration. OTHER LOGS syslog-ng For syslog-ng 2.x, add the following lines to syslog-ng.conf: # pass only entries with auth+authpriv facilities from programs other than sshguard filter sshlogs { facility(auth, authpriv) and not match("sshguard"); }; # pass to this process with this template (avoids <ID> prefixes) destination sshguardproc { program("/usr/local/sbin/sshguard" template("$DATE $FULLHOST $MESSAGE\n")); }; log { source(src); filter(sshlogs); destination(sshguardproc); }; For syslog-ng 3.x, add the following lines to syslog-ng.conf: # enable 3.x mode @version:3.0 # pass only entries with auth+authpriv facilities from programs other than sshguard filter f_sshguard { facility(auth, authpriv) and not program("sshguard"); }; # pass entries built with this format destination sshguard { program("/usr/sbin/sshguard" template("$DATE $FULLHOST $MSGHDR$MESSAGE\n") ); }; log { source(src); filter(f_sshguard); destination(sshguard); }; After restarting syslog-ng, SSHGuard should start as soon as a log en- try with facility auth or authpriv arrives. If you are monitoring ser- vices other than sshd, add the appropriate log facilities to sys- log-ng.conf. metalog Add the following lines to metalog.conf: Stuff to protect from brute force attacks : # for ssh facility = "*" program = "sshd" # other services ... # log to /var/log/sshguard directory logdir = "/var/log/sshguard" After restarting metalog, log entries will appear in /var/log/sshguard. Use log polling to monitor the current log. BACKENDS SSHGuard can block attackers using one of several firewall backends that is selected at compile-time. WARNING: Read the documentation for your firewall. Make sure you fully under- stand each rule or command in the examples below before using them. They may need to be adjusted to suit your particular configuration. pf SSHGuard adds attackers to table <sshguard>. Create the table and block attackers by adding the following lines to the end of pf.conf: table <sshguard> persist block in proto tcp from <sshguard> After reloading the pf configuration, you can inspect the contents of the table using: # pfctl -t sshguard -T show ipfw SSHGuard creates and adds attackers to table 22. The table can be used to block attackers in your ruleset. For example: # ipfw add 5000 reset ip from table\(22\) to me You can inspect the contents of the table using: # ipfw table 22 list firewalld Blocked attackers are added to two ipsets named sshguard4 and ssh- guard6. The entries in the ipsets are blocked by default in the de- fault firewall zone. Additional firewall zones can be configured using: # firewall-cmd --zone=zone-name --permanent \ --add-rich-rule="rule source ipset=sshguard4 drop" # firewall-cmd --zone=zone-name --permanent \ --add-rich-rule="rule source ipset=sshguard6 drop" You can inspect the entries in the two ipsets using: # firewall-cmd --permanent --info-ipset=sshguard4 # firewall-cmd --permanent --info-ipset=sshguard6 ipset Blocked attackers are added to two ipsets named sshguard4 and ssh- guard6. Nothing is blocked by default, but can used as a source for iptables and other tools. E.g.: # iptables -I INPUT -m set --match-set sshguard4 src -j DROP # ip6tables -I INPUT -m set --match-set sshguard6 src -j DROP netfilter/iptables Create a chain for SSHGuard: # iptables -N sshguard # for IPv4 # ip6tables -N sshguard # for IPv6 Update the INPUT chain to also pass the traffic to the sshguard chain at the very end of its processing. Specify in --dport all the ports of services your sshguard protects. If you want to prevent attackers from doing any traffic to the host, remove the option completely: # block any traffic from abusers iptables -A INPUT -j sshguard ip6tables -A INPUT -j sshguard Or: # block abusers only for SSH, FTP, POP, IMAP services (use "multiport" module) iptables -A INPUT -m multiport -p tcp --destination-ports 21,22,110,143 -j sshguard ip6tables -A INPUT -m multiport -p tcp --destination-ports 21,22,110,143 -j sshguard Verify that you have NOT a default allow rule passing all ssh traffic higher in the chain. Verify that you have NOT a default deny rule blocking all ssh traffic in your firewall. In either case, you already have the skill to adjust your firewall setup. Here is a sample ruleset that makes sense: iptables -N sshguard # block whatever SSHGuard says be bad ... iptables -A INPUT -j sshguard # enable ssh, dns, http, https iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -p udp --dport 53 -j ACCEPT iptables -A INPUT -p tcp --dport 80 -j ACCEPT iptables -A INPUT -p tcp --dport 443 -j ACCEPT # and block everything else (default deny) iptables -P INPUT DROP When rebooting, most systems reset the firewall configuration by de- fault. To preserve your configuration, you usually use the ipta- bles-save and iptables-restore utilities. However, each Linux variant has its own "right way". nftables SSHGuard creates tables with a high priority and adds attackers to a set automatically. You can inspect the contents of the sets using: # nft list set ip sshguard attackers # nft list set ip6 sshguard attackers Moreover, you can display sshguard's tables with: # nft list table ip sshguard # nft list table ip6 sshguard TROUBLESHOOTING Is SSHGuard configured correctly? Check that the correct FILES (or LOGREADER) and BACKEND are set in ssh- guard.conf. Is SSHGuard running? SSHGuard spawns a pipeline of cooperating processes. You can verify that SSHGuard is started correctly by viewing your process list using ps or top. Shown here are the processes associated with an example con- figuration: /bin/sh /opt/sshguard/sbin/sshguard tail -F -n 0 /tmp/log.txt /opt/sshguard/libexec/sshg-parser /opt/sshguard/libexec/sshg-blocker -a 30 -p 120 -s 1800 -N 128 -n 32 /bin/sh /usr/local/libexec/sshg-fw-null In order: • SSHGuard, installed in /opt/sshguard, is being interpreted by /bin/sh. • SSHGuard launched tail -F -n 0, which is monitoring /tmp/log.txt. • The default parser sshg-parser is running. • The blocker is running with options -a 30 -p 120 -s 1800 -N 128 -n 32. • The firewall sshg-fw-null is running. The null backend doesn't ac- tually block any attacks. Is SSHGuard recognizing attacks? SSHGuard recognizes attacks by parsing log messages. The format of log messages can occasionally change. If you are using the default, built-in attack parser, you can check if SSHGuard recognizes your at- tacks by running: $ cat /var/log/auth.log | %PREFIX%/libexec/sshg-parser -a Log messages that are recognized as attacks are prefixed with a '*' at the beginning of each line. If a log message that should be recognized as an attack is not, consider reporting it. EXAMPLES Ignore FILES and monitor these files instead: # sshguard /var/log/auth.log /var/log/maillog SEE ALSO sshguard(8) 2.4 August 27, 2020 SSHGUARD-SETUP(7)
NAME | DESCRIPTION | OTHER LOGS | BACKENDS | TROUBLESHOOTING | EXAMPLES | SEE ALSO
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