CVE-2025-9891 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the User Sync – Remote User Sync plugin for WordPress, developed by cyberlord92. This vulnerability exists in all versions up to and including 1.0.2 due to missing or incorrect nonce validation in the mo_user_sync_form_handler() function. Nonce validation is a security mechanism used to ensure that requests made to a web application are intentional and originate from legitimate users. The absence or improper implementation of this validation allows an attacker to craft a malicious request that, if executed by an authenticated site administrator (e.g., by clicking a link), can trigger the deactivation of the plugin without the administrator’s consent. The vulnerability requires user interaction (UI:R) but no authentication (PR:N) from the attacker, and it can be exploited remotely (AV:N). The impact is limited to integrity, as the attacker can alter the state of the plugin (deactivate it), but there is no direct impact on confidentiality or availability. The CVSS v3.1 base score is 4.3, categorized as medium severity. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability falls under CWE-352, which is a common web security weakness related to CSRF attacks. Given the widespread use of WordPress and the popularity of plugins for user synchronization, this vulnerability could be leveraged to disrupt administrative functions on affected sites, potentially impacting site management and security posture.

For European organizations using WordPress with the User Sync plugin, this vulnerability could lead to unauthorized deactivation of the plugin, disrupting user synchronization processes. This disruption may cause administrative overhead, potential loss of synchronization between user directories, and could indirectly affect access control and user management workflows. While the vulnerability does not directly expose sensitive data or cause denial of service, the ability to deactivate a security-related plugin without authorization could be exploited as part of a broader attack chain, especially in environments where user synchronization is critical for compliance or operational continuity. Organizations in sectors with strict regulatory requirements (e.g., finance, healthcare, government) could face compliance risks if user management is compromised. The requirement for an administrator to be tricked into clicking a malicious link means that social engineering defenses and user awareness are critical in mitigating impact.

1. Immediate mitigation should include disabling or uninstalling the User Sync plugin until a secure patched version is released. 2. Monitor official channels from the plugin developer and WordPress security advisories for updates or patches addressing CVE-2025-9891. 3. Implement strict Content Security Policy (CSP) headers and SameSite cookie attributes to reduce the risk of CSRF attacks. 4. Educate site administrators on the risks of clicking unsolicited links, especially those that could trigger administrative actions. 5. Employ web application firewalls (WAFs) with rules designed to detect and block CSRF attack patterns targeting WordPress plugins. 6. Review and harden WordPress administrative workflows to include multi-factor authentication and session management best practices, reducing the risk of session hijacking or misuse. 7. Conduct regular security audits of installed plugins and their configurations to identify and remediate vulnerabilities proactively.