User Sync – Remote User Sync <= 1.0.2 - Cross-Site Request Forgery to Plugin Deactivation
Strategic Overview
- Status
- Patched in 1.0.3
- Affected Plugin
- User Sync
- Affected Version
<= 1.0.2- CVSS
- 4.3Medium
- Weakness type
- CWE-352 · Cross-Site Request Forgery (CSRF)
- CVE
CVE-2025-9891
At a glance
CVE-2025-9891 is a medium-severity Cross-Site Request Forgery (CSRF) vulnerability in the User Sync WordPress plugin, affecting versions <= 1.0.2. It carries a CVSS score of 4.3 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 1.0.3; sites on affected versions should update now. Disclosed September 2025, reported by Jonas Benjamin Friedli.
Vulnerability Overview
The User Sync – Remote User Sync plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 1.0.2. This is due to missing or incorrect nonce validation on the mo_user_sync_form_handler() function. This makes it possible for unauthenticated attackers to deactivate the plugin via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site.
CWE-352: Cross-Site Request Forgery (CSRF)
User Sync <= 1.0.2 carries this weakness at mo_user_sync_form_handler(), and reaching it takes a caller who can reach the endpoint. Cross-site request forgery abuses the fact that browsers attach a victim's cookies to any request, so a state-changing action that only checks who you are, not whether you meant to act, can be triggered from another site.
An attacker who gets a logged-in user to load a crafted page can perform that action as them, with the impact scaling to whatever the victim's role is allowed to do. For User Sync the fix is 1.0.3: builds <= 1.0.2 are affected, anything from 1.0.3 onward is not.
Remediation
Update to version 1.0.3, or a newer patched version
How does WordSec protect against this?
The attempt arrives as an ordinary request to User Sync: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: User Sync 1.0.3 closes this, and updating the plugin is the step that ends it.
- Firewall
- Alerts
External References
Vulnerability data © Defiant, Inc., provided under the Wordfence Intelligence T&C