CVE-2025-9891 identifies a Cross-Site Request Forgery (CSRF) vulnerability in the User Sync – Remote User Sync WordPress plugin 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. Nonces in WordPress are security tokens used to verify that requests originate from legitimate users and prevent unauthorized actions. The absence or improper implementation of nonce validation allows attackers to craft malicious requests that, when executed by an authenticated administrator (via clicking a link or visiting a malicious webpage), can trigger the deactivation of the plugin without the administrator’s explicit consent. This attack vector requires no prior authentication by the attacker but does require user interaction from an administrator. The vulnerability affects the integrity of the plugin’s operation by allowing unauthorized deactivation, potentially disrupting user synchronization features or weakening security postures that depend on the plugin. The CVSS v3.1 base score is 4.3 (medium), reflecting the network attack vector, low complexity, no privileges required, but requiring user interaction and limited impact on integrity only. No known exploits have been reported in the wild as of the publication date. The vulnerability was reserved on 2025-09-02 and published on 2025-09-17. No patches or updates are currently linked, so mitigation may require manual intervention or plugin updates once available.

The primary impact of this vulnerability is the unauthorized deactivation of the User Sync plugin on WordPress sites, which can disrupt user synchronization processes between remote systems and the WordPress installation. This disruption could lead to administrative overhead, potential loss of synchronization functionality, and weakening of security controls that rely on the plugin’s operation. While the vulnerability does not directly compromise confidentiality or availability, the integrity of site management is affected. Attackers exploiting this vulnerability could cause confusion or downtime in user management workflows, potentially opening indirect avenues for further exploitation if user synchronization is critical for access control or auditing. Organizations relying on this plugin for user management, especially those with multiple administrators or complex user synchronization needs, may experience operational impacts. The requirement for administrator interaction limits widespread automated exploitation but targeted attacks against high-value WordPress administrators remain a concern.

To mitigate this vulnerability, organizations should immediately verify if they are using the User Sync – Remote User Sync plugin version 1.0.2 or earlier and plan to update to a patched version once released by the vendor. In the absence of an official patch, administrators can implement manual nonce validation in the mo_user_sync_form_handler() function to ensure requests are legitimate. Additionally, administrators should be trained to avoid clicking on suspicious links and to verify the legitimacy of requests that trigger plugin deactivation or other critical actions. Employing web application firewalls (WAFs) with rules to detect and block CSRF attack patterns targeting the plugin’s endpoints can provide temporary protection. Limiting administrative access to trusted networks or using multi-factor authentication can reduce the risk of successful exploitation. Regular monitoring of plugin status and audit logs can help detect unauthorized deactivation attempts promptly. Finally, maintaining a robust backup and recovery plan ensures quick restoration if the plugin is deactivated maliciously.