CVE-2024-3558 is a stored cross-site scripting vulnerability identified in the Custom Field Suite plugin for WordPress, maintained by mgibbs189. The vulnerability affects all versions up to and including 2.6.7. It stems from improper neutralization of input during web page generation, specifically insufficient sanitization and escaping of the 'cfs[post_title]' parameter. Authenticated users with contributor-level access or higher can exploit this flaw by injecting arbitrary JavaScript code into posts or pages. Because the malicious script is stored persistently, it executes in the context of any user who views the infected content, potentially compromising user sessions, stealing credentials, or performing unauthorized actions on behalf of users. The vulnerability does not require user interaction beyond viewing the page and has a CVSS 3.1 base score of 6.4, reflecting a medium severity level. The attack vector is network-based, with low attack complexity, requiring privileges but no user interaction. The scope is changed because the vulnerability can affect other users beyond the attacker. No patches or official fixes are currently linked, and no known exploits have been observed in the wild, but the risk remains significant due to the widespread use of WordPress and the plugin. Mitigation requires either updating the plugin when a patch is available or implementing strict input validation and output encoding on affected parameters.

The impact of CVE-2024-3558 is primarily on the confidentiality and integrity of affected WordPress sites. Exploitation allows attackers with contributor-level access to inject persistent malicious scripts that execute in the browsers of site visitors and administrators. This can lead to session hijacking, theft of authentication tokens, unauthorized actions performed with victim privileges, defacement, or distribution of malware. Although availability is not directly affected, the reputational damage and potential data breaches can be severe. Organizations relying on the Custom Field Suite plugin for content management face risks of compromised user accounts and data leakage. Given WordPress's extensive use worldwide, especially by small to medium enterprises, bloggers, and content-heavy sites, the vulnerability could be leveraged in targeted attacks or broader campaigns. The requirement for authenticated access limits exploitation to insiders or compromised accounts but does not eliminate risk, as contributor-level permissions are common in collaborative environments.

Organizations should immediately audit their WordPress installations to identify use of the Custom Field Suite plugin and verify the version in use. Until an official patch is released, administrators should restrict contributor-level access to trusted users only and consider temporarily disabling the plugin if feasible. Implementing Web Application Firewall (WAF) rules to detect and block suspicious input patterns targeting the 'cfs[post_title]' parameter can reduce risk. Additionally, site owners should enforce strict Content Security Policies (CSP) to limit script execution from untrusted sources. Regularly monitoring logs for unusual activity and scanning for injected scripts on pages can help detect exploitation attempts. When a patch becomes available, prompt updating is critical. Developers maintaining custom themes or plugins should review their input sanitization and output encoding practices to prevent similar vulnerabilities. Employing security plugins that harden WordPress installations and conducting periodic security assessments will further reduce exposure.