Threat actors have started hacking WordPress websites by exploiting a critical vulnerability in the WooCommerce Payments plugin.

A fully integrated payment solution developed by Automattic, the plugin has more than 600,000 active installations, WordPress tracking data shows.

Tracked as CVE-2023-28121 (CVSS score of 9.8) and patched in plugin version 5.6.2 on March 23, the exploited vulnerability allows an unauthenticated attacker to compromise an administrator’s account and take full control of a vulnerable website.

While there were no signs of in-the-wild exploitation of the bug when the patch was released, malicious attacks targeting unpatched versions of the WooCommerce Payments plugin have been ongoing for the past week, WordPress security firm Defiant reports.

“Large-scale attacks against the vulnerability, assigned CVE-2023-28121, began on Thursday, July 14, 2023 and continued over the weekend, peaking at 1.3 million attacks against 157,000 sites on Saturday, July 16, 2023,” Defiant says.

The campaign, which focuses on a small set of websites, started with an increase in plugin enumeration requests that were searching for a specific file in the plugin’s directory.

While the requests were distributed over thousands of IP addresses, most of the observed attacks came from a set of seven IP addresses, Defiant notes.

All the observed exploits targeting CVE-2023-28121 contained a header that “causes vulnerable sites to treat any additional payloads as coming from an administrative user”. Many of these requests, Defiant says, attempted to leverage admin privileges to install the WP Console plugin, to gain code execution.

“Once the WP Console plugin is installed, attackers use it to execute malicious code and place a file uploader in order to establish persistence,” Defiant says.

All sites running WooCommerce Payments versions 4.8.0 through 5.6.1 are vulnerable to CVE-2023-28121. According to WordPress data, more than 60% of sites run a plugin version above 5.9.x, so it is unclear how many websites are vulnerable.

Site administrators are advised to update their WooCommerce Payments installations to a patched version as soon as possible, especially since exploits targeting CVE-2023-28121 and technical details on the vulnerability have been public for several weeks.

“These attacks demonstrate significantly more sophistication than similar attacks we’ve seen in the past, including reconnaissance ahead of the main wave of attacks and multiple methods of maintaining persistence using functionality available to administrator-level users,” Defiant notes.

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https://www.securityweek.com/wordpress-sites-hacked-via-critical-vulnerability-in-woocommerce-payments-plugin/