More than 200,000 WordPress websites are exposed to ongoing attacks targeting a critical vulnerability in the Ultimate Member plugin.
Designed to make it easy for users to register and log in on sites, the plugin allows site owners to add user profiles, define roles, create custom form fields and member directories, and more.
Tracked as CVE-2023-3460 (CVSS score of 9.8), the recently identified security defect in Ultimate Member allows attackers to add a new user account to the administrators group.
Some of the plugin’s users have observed the creation of rogue accounts and reported them this week, but the attacks appear to have been ongoing at least since the beginning of June.
According to WordPress security firm WPScan, the issue is rooted in a conflict between the plugin’s blocklist logic and the way WordPress treats metadata keys.
Ultimate Member uses blocklists to store metadata keys that users should not manipulate and checks these lists whenever users attempt to register these keys when creating accounts.
Due to the difference in operation between the plugin and WordPress, attackers were able to trick the plugin into updating metadata keys, including one that stores user role and capabilities, WPScan explains. The company provides indicators of compromise (IoCs) associated with the observed attacks.
The plugin’s maintainers, who describe the issue as a privilege escalation bug, have attempted to address it in the last two versions of Ultimate Member, but they have reportedly failed to fully patch it. However, they did acknowledge the ongoing in-the-wild exploitation.
Site owners are advised to disable Ultimate Member to prevent exploitation of the vulnerability. They should also audit all administrator roles on their sites, to identify rogue accounts.