CVE-2024-3559 is a stored cross-site scripting (XSS) vulnerability identified in the Custom Field Suite plugin for WordPress, developed by mgibbs189. The vulnerability exists in all versions up to and including 2.6.7 due to improper neutralization of input during web page generation, specifically via the 'cfs[post_content]' parameter. This parameter lacks sufficient input sanitization and output escaping, allowing authenticated users with contributor-level privileges or higher to inject arbitrary JavaScript code into pages. When other users access these compromised pages, the injected scripts execute in their browsers, potentially leading to session hijacking, privilege escalation, or unauthorized actions performed on behalf of the victim. The vulnerability is categorized under CWE-79, indicating cross-site scripting issues. The CVSS v3.1 base score is 6.4, reflecting a medium severity level, with an attack vector of network, low attack complexity, privileges required (low), no user interaction needed, and a scope change. The impact primarily affects confidentiality and integrity, with no direct availability impact. No public exploits have been reported yet, but the vulnerability poses a significant risk due to the common use of the plugin and the ease of exploitation by authenticated users. The vulnerability's presence in a widely used WordPress plugin makes it a notable threat to many websites relying on this plugin for custom field management.

The primary impact of CVE-2024-3559 is the compromise of confidentiality and integrity of affected WordPress sites. Attackers with contributor-level access can inject malicious scripts that execute in the browsers of site visitors or administrators, potentially leading to session hijacking, theft of sensitive information, unauthorized actions, or further compromise of the site. This can damage the reputation of organizations, lead to data breaches, and facilitate lateral movement within the site or network. Since the vulnerability requires authenticated access, the risk is somewhat mitigated by the need for contributor-level permissions; however, many WordPress sites allow such roles for content creators or editors, increasing the attack surface. The vulnerability does not impact availability directly but can be leveraged as part of broader attack chains. Organizations relying on the Custom Field Suite plugin are at risk of targeted attacks, especially if they have multiple contributors or less stringent access controls. The scope of affected systems is broad given the popularity of WordPress and the plugin, making this a significant concern for web administrators globally.

1. Immediate upgrade: Apply any available patches or updates from the plugin developer mgibbs189 once released. Monitor official channels for updates. 2. Access control tightening: Restrict contributor-level and higher permissions to trusted users only, minimizing the number of users who can exploit this vulnerability. 3. Input validation and sanitization: Implement additional server-side input validation and output escaping for the 'cfs[post_content]' parameter via custom code or security plugins until an official patch is available. 4. Web Application Firewall (WAF): Deploy or update WAF rules to detect and block malicious payloads targeting this parameter. 5. Monitoring and logging: Enable detailed logging of user inputs and monitor for suspicious activity related to content submissions or modifications. 6. User education: Train contributors and editors on safe content practices and the risks of injecting untrusted content. 7. Disable or replace the plugin: If patching is not immediately possible, consider disabling the Custom Field Suite plugin or replacing it with a secure alternative. 8. Regular security audits: Conduct periodic security reviews of WordPress plugins and user roles to identify and mitigate similar risks proactively.