Security researchers have detected a massive campaign that scanned close to 1.6 million WordPress sites for the presence of a vulnerable plugin that allows uploading files without authentication.
The attackers are targeting the Kaswara Modern WPBakery Page Builder, which has been abandoned by its author before receiving a patch for a critical severity flaw tracked as CVE-2021-24284.
While the size of the campaign is impressive, with 1,599,852 unique sites being targeted, only a small portion of them are running the vulnerable plugin.
Researchers at Defiant, the maker of the Wordfence security solution for WordPress, observed an average of almost half a million attack attempts per day against customer sites they protect.
Indistinct large-scale attacks
Based on Wordfence telemetry data, the attacks started on July 4 and continue to this day. and are still ongoing today at an average of 443,868 attempts every day.
Daily attacks captured and blocked by Wordfence
The attacks originate from 10,215 distinct IP addresses, with some having generated millions of requests while others are limited to lower numbers, the reearchers say.
IP addresses launching the attacks (Wordfence)
The attackers send a POST request to ‘wp-admin/admin-ajax/php’, attempting to use the plugin’s ‘uploadFontIcon’ AJAX function to upload a malicious ZIP payload that contains a PHP file.
Some filenames the attackers use for the ZIP payloads are ‘inject.zip’, ‘king_zip.zip’, ‘null.zip’, ‘plugin.zip’, and ‘***_young.zip’.
If you’re still using the Kaswara Modern WPBakery Page Builder Addons plugin, you should remove it immediately from your WordPress site.
If you’re not using the plugin, you are still recommended to block the IP addresses of the attackers. For more details on the indicators and the most prolific sources of requests, check out Wordfence’s blog.