CVE-2025-5336 is a Stored Cross-Site Scripting (XSS) vulnerability identified in the Click to Chat plugin developed by HoliThemes for WordPress. This vulnerability affects all versions up to and including version 4.22. The root cause is improper neutralization of input during web page generation, specifically involving the 'data-no_number' parameter. Insufficient input sanitization and output escaping allow an authenticated attacker with Contributor-level access or higher to inject arbitrary malicious scripts into pages generated by the plugin. These scripts execute in the context of any user who accesses the compromised page, potentially leading to session hijacking, privilege escalation, or unauthorized actions performed on behalf of the victim user. The vulnerability does not require user interaction beyond visiting the injected page, and the attacker must have at least Contributor privileges, which are commonly assigned to trusted users who can create and edit content but cannot publish it directly. The CVSS v3.1 base score is 6.4 (medium severity), with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), privileges required (PR:L), no user interaction (UI:N), scope changed (S:C), and low impact on confidentiality and integrity (C:L, I:L) but no impact on availability (A:N). No known exploits are currently reported in the wild, and no official patches have been published yet. The vulnerability was publicly disclosed on June 14, 2025, with the initial reservation date on May 29, 2025. This issue is classified under CWE-79, which covers improper neutralization of input leading to XSS attacks. Given the widespread use of WordPress and the popularity of the Click to Chat plugin for customer engagement, this vulnerability poses a significant risk to websites that rely on this plugin, especially those with multiple contributors or editors who have elevated privileges.

For European organizations, the impact of this vulnerability can be substantial, particularly for businesses and institutions that use WordPress with the Click to Chat plugin to manage customer interactions or internal communications. Exploitation could lead to unauthorized script execution in the browsers of site visitors or administrators, enabling attackers to steal session cookies, deface websites, redirect users to malicious sites, or perform actions on behalf of legitimate users. This can result in data breaches, reputational damage, and potential regulatory non-compliance under GDPR due to unauthorized access or exposure of personal data. The requirement for Contributor-level privileges means that insider threats or compromised user accounts could be leveraged to exploit this vulnerability. Since the scope is changed (S:C), the vulnerability can affect resources beyond the initially compromised component, potentially impacting the entire WordPress site and its users. The lack of known exploits in the wild currently reduces immediate risk, but the medium severity score and ease of exploitation (low complexity, network accessible) suggest that attackers could develop exploits rapidly. Organizations with multi-user WordPress environments, especially those in sectors like e-commerce, finance, healthcare, and government, where customer trust and data protection are critical, face higher risks. Additionally, the persistent nature of stored XSS means that injected scripts remain active until removed, increasing the window of exposure.

1. Restrict Contributor and higher privileges strictly: Review and minimize the number of users with Contributor-level or higher access to the WordPress backend, ensuring only trusted personnel have such privileges. 2. Implement Web Application Firewall (WAF) rules: Deploy WAF solutions that can detect and block malicious payloads targeting the 'data-no_number' parameter or typical XSS attack patterns in HTTP requests. 3. Conduct regular plugin audits: Continuously monitor installed plugins for updates or security advisories from HoliThemes and the WordPress community. Since no official patch is currently available, consider temporarily disabling or replacing the Click to Chat plugin with a secure alternative until a fix is released. 4. Harden input validation and output encoding: If custom development is possible, apply additional server-side input validation and output escaping for parameters related to chat or user-generated content. 5. Monitor logs and user activity: Implement logging and alerting for suspicious activities, such as unusual content submissions or script injections by users with Contributor or higher roles. 6. Educate users: Train content contributors and administrators on security best practices, including recognizing phishing attempts and the risks of privilege misuse. 7. Backup and recovery plans: Maintain up-to-date backups of WordPress sites to enable rapid restoration in case of compromise. 8. Segmentation and least privilege: Isolate critical WordPress instances and enforce least privilege principles to limit the impact of any successful exploitation.