CVE-2026-109216 in Meta Box Plugin
Summary
by MITRE • 10/29/2026
The Meta Box – A Framework for Dynamic Websites plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'profile_background[<attacker-chosen key>]' parameter in all versions up to, and including, 5.15.2 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with subscriber-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Exploitability depends on a consuming plugin or theme built on Meta Box that exposes the background field to lower-privileged users and renders stored values via the rwmb_the_value()/format_single_value() pattern; the effective minimum privilege is whatever role that consumer permits, demonstrated at Subscriber level.
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified in The Meta Box – A Framework for Dynamic Websites plugin for WordPress represents a significant security risk within the ecosystem of dynamic website development tools. This specific flaw allows for Stored Cross-Site Scripting, commonly referred to as XSS, which is classified under CWE-79 in the Common Weakness Enumeration standards. The root cause lies in insufficient input sanitization and output escaping mechanisms when handling the profile_background parameter with attacker-chosen keys. In a typical WordPress environment, plugins that handle user-generated content must rigorously validate and escape data before storing it or rendering it to prevent malicious scripts from being executed by unsuspecting users.
The technical flaw manifests specifically through the way the plugin processes background fields associated with user profiles. When an authenticated attacker submits form data containing script payloads within these fields, the application fails to adequately sanitize the input on the server side nor does it properly escape the output when rendering the value later. This lack of defensive coding practices means that malicious JavaScript code is persisted in the database rather than being neutralized or encoded into safe text entities. The vulnerability affects all versions up to and including 5.15.2, indicating a systemic issue within the framework's handling of dynamic fields during this period.
The operational impact of this vulnerability extends beyond simple data corruption because it enables persistent attacks against site visitors. Once the malicious script is stored in the database, it will execute whenever any user accesses a page that renders the compromised profile background field. This execution occurs in the context of the victim's browser session, potentially allowing attackers to steal cookies, hijack sessions, deface websites, or redirect users to phishing sites. The severity is compounded by the fact that exploitation requires only subscriber-level access and above, which are relatively low-privilege roles available to many registered users on public-facing WordPress installations.
Exploitability in this context is contingent upon specific architectural conditions within consuming plugins or themes built using Meta Box. The attack vector becomes effective when a consumer application exposes the background field to lower-privileged users and utilizes the rwmb_the_value() or format_single_value() functions for rendering stored values. These functions are designed to output data directly, and without proper escaping integration from the plugin developer, they serve as direct conduits for executing injected scripts. The demonstration of this vulnerability at the Subscriber level highlights that even minimal user privileges can lead to severe security breaches if input validation is not enforced consistently across all entry points.
From a threat intelligence perspective, this behavior aligns with ATT&CK technique T1059, specifically Command and Scripting Interpretation via JavaScript in web browsers. The persistence mechanism corresponds to T1187, where attackers establish footholds by modifying existing content within the application's data stores. This allows for long-term access without requiring repeated exploitation attempts, as each page load triggers the malicious payload automatically. Security professionals should recognize this pattern as a critical failure in input validation and output encoding protocols that are fundamental to web application security frameworks like OWASP Top Ten.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary action is to upgrade The Meta Box plugin to version 5.15.3 or later, where the developers have presumably implemented stricter sanitization and escaping routines for all dynamic fields. For organizations unable to update immediately due to compatibility constraints with consuming themes or plugins, manual code modifications may be necessary to enforce output encoding on any field that accepts user input from low-privilege roles. Additionally, implementing a Content Security Policy can help mitigate the impact of successful XSS attacks by restricting script execution sources and preventing unauthorized external resource loading.
Developers utilizing Meta Box should audit their custom implementations to ensure they adhere to WordPress coding standards for data validation and sanitization. This includes using appropriate escaping functions such as esc_html() or wp_kses_post() when outputting dynamic content, particularly in templates that render user profile information. Security testing procedures should incorporate automated scans targeting stored XSS vectors in all editable fields exposed to non-administrative users. Regular penetration testing focusing on input validation boundaries will help identify similar weaknesses before they can be exploited by malicious actors seeking to compromise site integrity or steal sensitive user data through session hijacking techniques.