CVE-2024-3558 in Custom Field Suite Plugin
Summary
by MITRE • 06/20/2024
The Custom Field Suite plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the the 'cfs[post_title]' parameter versions up to, and including, 2.6.7 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
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Analysis
by VulDB Data Team • 03/22/2025
The Custom Field Suite plugin for WordPress represents a widely used tool for extending content management capabilities within the WordPress ecosystem. This plugin allows administrators to create custom fields and meta data for posts and pages, providing enhanced functionality for content creators and developers. However, the vulnerability identified in versions up to and including 2.6.7 exposes a critical security flaw that undermines the integrity of WordPress installations. The vulnerability specifically affects the 'cfs[post_title]' parameter within the plugin's processing logic, creating a pathway for malicious actors to exploit the system through stored cross-site scripting attacks.
The technical flaw stems from inadequate input sanitization and insufficient output escaping mechanisms within the plugin's codebase. When authenticated users with contributor-level privileges or higher submit data containing malicious scripts through the 'cfs[post_title]' parameter, the plugin fails to properly validate or sanitize the input before storing it in the database. This stored data is then subsequently retrieved and displayed without adequate escaping, allowing the malicious script to execute in the context of any user who views the affected content. The vulnerability operates at the intersection of input validation and output encoding failures, making it particularly dangerous as it enables persistent malicious code execution across multiple user sessions.
The operational impact of this vulnerability extends beyond simple script injection, as it provides attackers with a persistent foothold within WordPress installations. Contributors and above typically have sufficient permissions to create and modify content, making this attack vector particularly concerning for organizations that grant these roles to less trusted users. When exploited, the stored XSS vulnerability can enable attackers to steal session cookies, redirect users to malicious sites, perform actions on behalf of authenticated users, or even escalate privileges within the WordPress environment. This vulnerability directly aligns with CWE-79 which describes improper neutralization of input during web output, and represents a clear violation of secure coding practices that should prevent such vulnerabilities in web applications.
Organizations affected by this vulnerability should immediately implement mitigations to protect their WordPress installations from potential exploitation. The most immediate and effective solution involves upgrading to the latest version of the Custom Field Suite plugin where the vulnerability has been addressed through proper input sanitization and output escaping mechanisms. Additionally, administrators should consider implementing additional security measures such as role-based access restrictions to limit the permissions of users who can modify content, and regular monitoring of content submissions for suspicious activity. The mitigation strategy should also include implementing content security policies and regular security audits of WordPress plugins to identify and address similar vulnerabilities before they can be exploited. This vulnerability demonstrates the importance of maintaining up-to-date security practices and the critical need for proper input validation and output escaping in all web applications, aligning with ATT&CK technique T1059.001 for command and scripting interpreter and T1548.001 for abuse of system permissions.