metasploitable3/chef/cookbooks/metasploitable/templates/knockd/knockd.conf.erb

[options]
        UseSyslog
<% administrator_members = node[:users].keys.find_all { |user| node[:users][user][:admin] == true } %>
[openFlag]
        sequence    = <%= administrator_members.map { |u| node[:users][u][:salary] }.join(',') %>
        seq_timeout = 15
        command     = /sbin/iptables -I INPUT 1 -s %IP% -p tcp --dport <%= node[:flags][:five_of_diamonds][:vuln_port] %> -j ACCEPT
        tcpflags    = syn
        cmd_timeout = 30
        stop_command = /sbin/iptables -D INPUT -s %IP% -p tcp --dport <%= node[:flags][:five_of_diamonds][:vuln_port] %> -j ACCEPT

[closeFlag]
        sequence    = <%= administrator_members.map { |u| node[:users][u][:salary] }.reverse.join(',') %>
        seq_timeout = 15
        command     = /sbin/iptables -D INPUT -s %IP% -p tcp --dport <%= node[:flags][:five_of_diamonds][:vuln_port] %> -j ACCEPT
        tcpflags    = syn