Hackers are actively exploiting a critical vulnerability in the WooCommerce Wholesale Lead Capture premium plugin for WordPress to upload a PHP backdoor.
The flaw is tracked as CVE-2026-27540 and impacts plugin versions 2.0.3.1 and older. It is an unauthenticated arbitrary file-upload vulnerability discovered by security researcher Teemu Saarentaus.
An attacker can exploit it to upload PHP webshells and execute code, potentially leading to a complete site compromise.
From a technical standpoint, the flaw is caused by exposing an unauthenticated AJAX action named wwlc_file_upload_handler, which checks file extensions against an allowlist supplied through the user-controlled file_settings request parameter.
This allows adding ‘php’ to the permitted file types, making the plugin accept PHP executable file uploads.
The vulnerability was addressed in version 2.0.3.2 of the WooCommerce Wholesale Lead Capture plugin, released on February 20.
However, WordPress security company Defiant is warning that its Wordfence web application firewall blocked over 100,000 attacks linked to CVE-2026-27540.
Wordfence reports that exploitation activity spiked between June 4 and June 17, and on July 1 and August 30.
During the attacks, the hackers upload a webshell that conducts reconnaissance but can also introduce additional payloads.
“The attacker submits a request to the wwlc_file_upload_handler AJAX action containing a forged file_settings parameter and a malicious file with a .php extension,” Wordfence explains.
“The uploaded shell.php is a PHP webshell that reports host details and provides a browser-based upload form for writing additional malicious files to the site.”
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Source: Wordfence
Wordfence provides a set of high-offender IP addresses that deployed tens of thousands of exploitation attempts. Administrators are recommended to add them to a blocklist and upgrade to plugin version 2.0.3.2 or later that addresses the security problem.
The researchers advise checking upload directories for unexpected or recently created PHP files, examining logs for requests to /wp-admin/admin-ajax.php invoking wwlc_file_upload_handler, and removing unknown administrator accounts.
If compromise is confirmed, the recommended action is to restore the website from a safe backup, as removing all persistence mechanisms, users, and backdoors may be complicated.
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