CVE-2023-4388 is a stored Cross-Site Scripting (XSS) vulnerability identified in the EventON WordPress plugin versions prior to 2.2. The vulnerability arises because the plugin fails to properly sanitize and escape certain settings inputs. This flaw allows users with high privileges, such as administrators, to inject malicious scripts into the plugin's stored settings. Notably, this exploitation is possible even when the WordPress capability 'unfiltered_html' is disabled, which is a common restriction in multisite WordPress environments to prevent untrusted HTML content. The vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. The CVSS v3.1 base score is 4.8 (medium severity), with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), high privileges required (PR:H), user interaction required (UI:R), scope changed (S:C), and low impact on confidentiality and integrity (C:L, I:L), with no impact on availability (A:N). Exploitation requires an authenticated user with high privileges to perform actions that inject malicious scripts, which then execute in the context of other users viewing the affected content. Although no known exploits are currently reported in the wild, the vulnerability poses a risk in environments where multiple administrators or privileged users interact with the EventON plugin settings. The scope change indicates that exploitation could affect components beyond the initially vulnerable plugin, potentially impacting the entire WordPress site or multisite network. The vulnerability is particularly relevant for WordPress multisite deployments where unfiltered_html is restricted but administrative users still have access to EventON settings. Since no patch links are provided, it is assumed that a fixed version 2.2 or later addresses this issue, and upgrading is recommended once available.

For European organizations using WordPress with the EventON plugin, especially in multisite configurations, this vulnerability could lead to stored XSS attacks that compromise the integrity and confidentiality of administrative sessions. Attackers with administrative privileges could inject malicious JavaScript that executes in the browsers of other administrators or privileged users, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of victims. Although the vulnerability does not directly affect availability, the compromise of administrative accounts could lead to broader site defacement, data leakage, or further exploitation. This risk is heightened in organizations with multiple administrators managing event-related content or scheduling via EventON. Given the medium CVSS score and the requirement for high privileges and user interaction, the threat is moderate but significant in environments where administrative controls are distributed or where insider threats exist. The vulnerability could also be leveraged as a stepping stone for lateral movement within the WordPress environment or to implant persistent malicious code. European organizations in sectors with strict data protection regulations (e.g., GDPR) may face compliance risks if such an attack leads to data breaches or unauthorized data access.

1. Upgrade the EventON plugin to version 2.2 or later as soon as it becomes available, since the vulnerability affects versions prior to 2.2. 2. Until an upgrade is possible, restrict administrative access to the EventON plugin settings to only the most trusted users to minimize the risk of malicious input. 3. Implement Content Security Policy (CSP) headers to limit the execution of unauthorized scripts within the WordPress admin interface. 4. Regularly audit and sanitize all plugin settings and stored data related to EventON, manually removing any suspicious or unexpected scripts or HTML content. 5. Employ Web Application Firewalls (WAF) with rules designed to detect and block stored XSS payloads targeting WordPress plugins. 6. Monitor administrative user activity logs for unusual behavior that might indicate exploitation attempts. 7. Educate administrators about the risks of stored XSS and the importance of cautious input handling, especially when multiple admins manage the same WordPress instance. 8. Consider isolating or sandboxing the EventON plugin environment if possible, to limit the scope of any potential compromise. 9. Ensure that WordPress core and all other plugins are kept up to date to reduce the attack surface.