CVE-2024-9428 in Popup Builder Plugin
Summary
by MITRE • 12/12/2024
The Popup Builder WordPress plugin before 4.3.5 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).
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Analysis
by VulDB Data Team • 05/07/2025
The vulnerability identified as CVE-2024-9428 affects the Popup Builder WordPress plugin version 4.3.4 and earlier, representing a critical security flaw that enables stored cross-site scripting attacks. This issue specifically targets high-privilege users such as administrators who possess the capability to modify plugin settings, even in environments where the unfiltered_html capability has been restricted. The vulnerability stems from inadequate input sanitization and output escaping mechanisms within the plugin's configuration handling processes. In multisite WordPress installations, where security restrictions are often more stringent, this flaw becomes particularly dangerous as it allows authenticated attackers with administrative privileges to inject malicious scripts into the plugin's settings that persist across user sessions.
The technical implementation of this vulnerability falls under CWE-79 - Improper Neutralization of Input During Web Page Generation, which specifically addresses the failure to properly sanitize user-supplied data before incorporating it into web pages. The flaw occurs when the plugin processes user inputs in its settings interface without applying appropriate sanitization filters or escaping mechanisms to prevent malicious script execution. This allows attackers to inject malicious JavaScript code through the plugin's configuration parameters, which then gets stored in the database and executed whenever the affected pages are loaded. The vulnerability is classified as stored XSS because the malicious payload is permanently saved within the application's data store rather than being executed through a single request.
From an operational perspective, this vulnerability presents a significant risk to WordPress multisite environments where administrative privileges are distributed across multiple users. Attackers can leverage this flaw to execute arbitrary JavaScript code in the context of any user's browser who accesses pages utilizing the affected plugin. The impact extends beyond simple script execution as it can lead to session hijacking, credential theft, data exfiltration, and potential privilege escalation within the WordPress environment. In a multisite setup, where the unfiltered_html capability is typically restricted to prevent XSS attacks, this vulnerability undermines the security model by allowing administrators to bypass these protections through the plugin's settings interface.
The attack vector requires an authenticated user with administrative privileges to the specific plugin, making it less likely to be exploited by casual attackers but still dangerous in environments where administrative accounts may be compromised. The vulnerability can be exploited by navigating to the plugin's settings page and inserting malicious JavaScript code into configurable fields that are not properly sanitized. This code then executes whenever the popup functionality is triggered or when the settings page is accessed by other administrators. The persistence of stored XSS attacks makes this vulnerability particularly concerning as the malicious code remains active until manually removed from the plugin's configuration.
Organizations should implement immediate mitigations including upgrading to Popup Builder version 4.3.5 or later, which contains the necessary sanitization and escaping fixes. Security administrators should also review plugin permissions and ensure that only trusted users have administrative access to the affected plugin. Additional defensive measures include implementing content security policies to limit script execution, monitoring for suspicious plugin configuration changes, and conducting regular security audits of WordPress installations. The vulnerability demonstrates the importance of proper input validation and output escaping in web applications, particularly in environments where privileged users can modify application settings. Organizations should also consider implementing automated scanning tools to detect similar vulnerabilities in other plugins and themes that may not have received timely security updates.