ModSecurity (also known as “modsec”) has proven itself useful in a variety of situations, and again this is true in assisting with WordPress brute force attempts resulting in a Denial of Service (DoS) attack. While a number of WordPress plugins exist to prevent such attacks, custom modsec rules can prevent such attacks for all WordPress installations on a server. Modsec immediately filters incoming HTTP requests, which assists against taxing server resources.
These rules will block access for the offending IP address for 5 minutes upon 10 failed login attempts over a 3 minute duration. These rules can be added to your custom modsec rules. To accomplish this, edit your custom modsec user rules and append the file with the rules provided below. For cPanel servers, this file is likely located at /usr/local/apache/conf/
# Setup brute force detection.
# React if block flag has been set.
SecRule user:bf_block "@gt 0" "deny,status:401,log,id:5000135,msg:'ip address blocked for 5 minutes, more than 10 login attempts in 3 minutes.'"
# Setup Tracking. On a successful login, a 302 redirect is performed, a 200 indicates login failed.
SecRule RESPONSE_STATUS "^302" "phase:5,t:none,nolog,pass,setvar:ip.bf_counter=0,id:5000136"
SecRule RESPONSE_STATUS "^200" "phase:5,chain,t:none,nolog,pass,setvar:ip.bf_counter=+1,deprecatevar:ip.bf_counter=1/180,id:5000137"
SecRule ip:bf_counter "@gt 10" "t:none,setvar:user.bf_block=1,expirevar:user.bf_block=300,setvar:ip.bf_counter=0"