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Vulnerability in Field Builder Plugin Exposes Over 2M WordPress Sites to Attacks

An XSS vulnerability in the Advanced Custom Fields WordPress plugin exposes more than 2 million sites to attacks.

A cross-site scripting (XSS) vulnerability in the Advanced Custom Fields WordPress plugin could be exploited to inject malicious scripts into websites.

Tracked as CVE-2023-30777, the vulnerability impacts both the free and paid versions of the plugin. Advanced Custom Fields has more than 2 million installs via the official WordPress app store.

The plugin provides site administrators with the ability to easily add fields to WordPress edit screens, posts, pages, and other site elements.

Identified by Patchstack security researcher Rafie Muhammad, CVE-2023-30777 is described as a high-severity reflected XSS bug impacting the plugin’s admin page.

“This could allow a malicious actor to inject malicious scripts, such as redirects, advertisements, and other HTML payloads into your website which will be executed when guests visit your site,” Patchstack notes in an advisory.

The flaw was identified in a function configured as an extra handler for a WordPress hook that has the same name, and which controls the CSS classes for the main body tag in the admin area.

The root cause of the issue is an improper sanitization of output value of the hook, which could lead to XSS if the function handler fails to properly sanitize the returned classes string.

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According to Patchstack, the vulnerability can be triggered on default plugin installations, either by unauthenticated attackers or by logged-in users with access to the plugin.

The security defect was identified on May 2 and reported to the vendor the same day. A patch was released two days later.

Advanced Custom Fields version 6.1.6 addresses the vulnerability for both free and paid customers. The fix was also included in version 5.12.6 of the plugin.

Users are advised to update their installations as soon as possible. Unpatched WordPress plugins are often exploited in malicious attacks to take over sites and infect their visitors with malware.

Related: Abandoned WordPress Plugin Abused for Backdoor Deployment

Related: Elementor Pro Plugin Vulnerability Exploited to Hack WordPress Websites

Related: Vulnerability in Popular Real Estate Theme Exploited to Hack WordPress Websites

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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