For the past 48 hours or so, I’ve been dealing with extreme server load issues, causing drastic slowdowns and ultimately causing my VPS to crash multiple times.
I found this was due to a DDoS attack on WordPress sites that exploits WP’s post/ping system, which is explained in more depth here.
The interim fix is to disable/redirect XMLRCP via htaccess or, if you’re running CloudFlare, to increase the level of security. I presume (hopefully) that an upcoming WP release will address this issue.
Here’s an htaccess solution that redirects those abusing this to a non-existent IP that worked for me (my server load immediately returned to a normal state):
RewriteRule ^xmlrpc\.php$ "http\:\/\/0\.0\.0\.0\/" [R=301,L]
This will probably cause issues with pinging and remote posting, so please consider it a temporary fix. If you notice your sites are running sluggishly, or that your server is continually crashing, this could be the cause.
To investigate further, check out your latest visitor log in cPanel — if you see something similar to what’s shown in the image below, you’re probably a victim.
If not, you’re probably unaffected, but it’s something to keep your eye out for!