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Attackers Scan 1.6 Million WordPress Sites for Vulnerable Plugin

Security researchers have detected a large 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 was abandoned by its author before receiving a patch for a critical severity flaw tracked as CVE-2021-24284. The vulnerability would allow an unauthenticated attacker to inject malicious JavaScript into sites using any version of the plugin and perform actions like uploading and deleting files, which could lead to a complete takeover of the site. While the size of the campaign is impressive, with 1,599,852 unique sites being targeted, only a small portion of them is 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. Based on Wordfence telemetry data, the attacks started on July 4 and are still ongoing today at an average of 443,868 attempts every day. The researchers say that the attacks have originated from 10,215 distinct IP addresses, with some generating millions of requests while others are limited to lower numbers.

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. This file, in turn, fetches the NDSW trojan, which injects code in legitimate JavaScript files present on the target sites to redirect visitors to malicious destinations like phishing and malware-dropping sites. Some filenames the attackers use for the ZIP payloads are ‘’, ‘’, ‘’, ‘’, and ‘***’. These files or the presence of the “; if(ndsw==” string in any JavaScript files indicates that the site has been infected.

Analyst Notes

Any remaining instances of the Kaswara Modern WPBakery Page Builder should be removed immediately from WordPress sites. If it is not being used, it is 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 linked below.

PSA: Sudden Increase In Attacks On Modern WPBakery Page Builder Addons Vulnerability