Millions of WordPress sites were attacked this week, said Defiant, the company behind the Wordfence firewall.
The sudden rise in attacks occurred when hackers discovered and began exploiting a 0day vulnerability in “File Manager, A WordPress plugin used on more than 700.000 websites.
0day allowed an attacker to upload malicious files to a site running an older version of File Manager.
It is not known how they discovered 0day, but all last week the hackers started looking for sites that had this add-on installed.
If the scan was successful, the attackers took advantage of the 0day and uploaded a web shell disguised as an image file to the victim's server. So they could access the site by adding it to a botnet.
The attacks started late, but intensified throughout the past week. Defiant detected attacks on 1 million WordPress sites as of Friday, September 4th.
In all, Defiant has blocked attacks on more than 1,7 million websites since September 1, when the attacks were first discovered.
The good news is that the File Manager developer team created and released an update for 0day the same day they learned about the attacks. Some administrators installed the update immediately, but as usual, there are others who did not.