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Websites Hacked via Zero-Day Flaws in WordPress Plugins

Zero-day flaws affecting several WordPress plugins have been exploited by malicious actors to plant backdoors and take control of vulnerable websites.

The attacks have been spotted by Wordfence, a company that specializes in protecting WordPress websites.

The firm’s investigation revealed that attackers had been exploiting previously unknown vulnerabilities in three WordPress plugins. The flaws, described as critical PHP object injection issues, affect the Appointments, Flickr Gallery, and RegistrationMagic-Custom Registration Forms plugins.

Attacks exploiting the zero-day vulnerability involved the creation of a file on targeted websites, but logs only showed a POST request to /wp-admin/admin-ajax.php, which made it look as if the file appeared out of nowhere, researchers said.

“This vulnerability allowed attackers to cause a vulnerable website to fetch a remote file (a PHP backdoor) and save it to a location of their choice. It required no authentication or elevated privileges. For sites running Flickr Gallery, the attackers only had to send the exploit as POST request to the site’s root URL. For the other two plugins, the request would go to admin-ajax.php,” Wordfence explained in a blog post.

The developers of the affected plugins were notified and they released updates to address the flaw. The security hole was patched in Appointments 2.2.2, Flickr Gallery 1.5.3 and RegistrationMagic

While the vulnerability is critical, the plugins are only used by roughly 8,000 (RegistrationMagic), 9,000 (Appointments) and 4,000 (Flickr Gallery) WordPress websites.

This means that the number of potentially impacted websites is small compared to other incidents involving WordPress plugins. Wordfence reported last month that it had identified malicious functionality in a plugin present on roughly 200,000 websites.

While plugin flaws can be dangerous, it’s even more dangerous when attackers exploit zero-day or recently patched vulnerabilities affecting WordPress itself. Tens of thousands of sites were hacked within days after the existence of the weakness came to light in February.

WordPress has been running a bug bounty program since this past spring and it has so far paid out rewards totaling thousands of dollars.

Related: WordPress Rushes to Fix Critical Zero-Day Vulnerability

Related: WordPress Delayed Disclosure of Critical Vulnerability

Related: Nine Vulnerabilities Patched in WordPress

Related: Unpatched WordPress Password Reset Flaw Disclosed

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.