WPScan is reporting a hacking campaign actively exploiting an unpatched vulnerability in the Ultimate Member plugin, which allows unauthenticated attackers to create new user accounts with administrative privileges and take over the site. The vulnerability has been assigned a CVSSv3.1 (Common Vulnerability Scoring System) score of 9.8 (Critical).
Automattic’s WP.cloud and Pressable.com hosting platforms picked up on a trend in compromised sites where each had rogue new administrators popping up. After further investigation they found a discussion on the WordPress.org support forums about a potential Privilege Escalation vulnerability in the plugin, as well as indications that it was already being actively exploited.
Ultimate Member, which is active on more than 200,000 WordPress sites, patched the plugin, but WPScan reports that it wasn’t sufficient.
“In response to the vulnerability report, the creators of the plugin promptly released a new version, 2.6.4, intending to fix the problem,” WPScan security researcher Marc Montpas said. “However, upon investigating this update, we found numerous methods to circumvent the proposed patch, implying the issue is still fully exploitable.
“Adding to the urgency of the situation, a look at our monitoring systems also confirmed attacks using this vulnerability were indeed happening in the wild.”
WPScan has identified more than a dozen IP addresses from which exploits are originating, common usernames for malicious accounts, and other indicators of compromise, such as malicious plugins, themes, and code. Check the security advisory if you believe you have been compromised.
Version 2.6.6 is the latest release from the Ultimate Member plugin but it is still believed to be vulnerable. WPScan recommends users disable the plugin until it has been adequately patched.