CVE-2026-39607: Filter Plus Auth Bypass Vulnerability

CVE-2026-39607 Overview

A Missing Authorization vulnerability has been identified in the Wpbens Filter Plus WordPress plugin (filter-plus). This vulnerability allows attackers to exploit incorrectly configured access control security levels, potentially enabling unauthorized access to protected functionality within WordPress sites using this plugin.

The vulnerability stems from broken access control mechanisms (CWE-862) that fail to properly verify user permissions before allowing access to sensitive plugin features. This type of vulnerability can enable unauthenticated or low-privileged users to perform actions that should be restricted to administrators or other authorized roles.

Critical Impact

Unauthorized users may be able to bypass access controls and execute privileged operations within WordPress sites running vulnerable versions of the Filter Plus plugin, potentially compromising site integrity and data security.

Affected Products

• Wpbens Filter Plus plugin for WordPress versions through 1.1.17

Discovery Timeline

• April 8, 2026 - CVE-2026-39607 published to NVD
• April 8, 2026 - Last updated in NVD database

Technical Details for CVE-2026-39607

Vulnerability Analysis

This vulnerability falls under the category of Broken Access Control, specifically Missing Authorization (CWE-862). The Filter Plus plugin fails to implement proper authorization checks on certain functionality, allowing users without appropriate permissions to access restricted features.

In WordPress plugin development, authorization checks typically involve verifying user capabilities using functions like current_user_can() or checking nonces for CSRF protection. When these checks are missing or improperly implemented, attackers can directly invoke privileged functionality by crafting specific requests to vulnerable endpoints.

The impact of this vulnerability depends on which specific functions lack proper authorization, but broken access control vulnerabilities in WordPress plugins can lead to unauthorized data modification, privilege escalation, or exposure of sensitive information.

Root Cause

The root cause of CVE-2026-39607 is the absence of proper authorization verification within the Filter Plus plugin. The plugin does not adequately check whether the requesting user has sufficient permissions before processing certain requests. This is a common security oversight in WordPress plugin development where AJAX handlers or form processors are exposed without proper capability checks.

WordPress provides built-in functions for authorization such as current_user_can(), check_ajax_referer(), and wp_verify_nonce(). When developers fail to implement these checks, or implement them incorrectly, users can bypass intended access restrictions.

Attack Vector

The attack vector for this vulnerability involves exploiting the incorrectly configured access control mechanisms in the Filter Plus plugin. An attacker would typically:

1. Identify endpoints or AJAX actions exposed by the plugin that lack proper authorization
2. Craft malicious requests targeting these unprotected endpoints
3. Execute privileged operations without having the required user role or permissions

Since no verified proof-of-concept code is available, the specific exploitation method should be referenced from the Patchstack Vulnerability Report for technical details on the vulnerable functionality.

Detection Methods for CVE-2026-39607

Indicators of Compromise

• Unexpected modifications to filter settings or plugin configurations
• Log entries showing AJAX requests to Filter Plus endpoints from unauthenticated or low-privileged users
• Unusual activity patterns involving the filter-plus plugin directory or its handlers

Detection Strategies

• Review WordPress access logs for unauthorized requests to Filter Plus AJAX endpoints
• Monitor for unusual administrative actions occurring without corresponding authenticated admin sessions
• Implement Web Application Firewall (WAF) rules to detect and block unauthorized access attempts to plugin endpoints

Monitoring Recommendations

• Enable verbose logging for WordPress AJAX handlers and review for anomalous access patterns
• Configure alerts for any modifications to plugin settings made outside of normal administrative workflows
• Regularly audit user activity logs for privilege escalation indicators

How to Mitigate CVE-2026-39607

Immediate Actions Required

• Update the Filter Plus plugin to a version newer than 1.1.17 once a patched version becomes available
• Temporarily disable the Filter Plus plugin if it is not critical to site operations until a patch is released
• Implement additional access controls at the web server or WAF level to restrict access to plugin endpoints
• Review site logs for any signs of exploitation

Patch Information

Users should monitor the WordPress plugin repository and the Patchstack Vulnerability Report for updates regarding an official security patch from the vendor. Ensure automatic updates are enabled for WordPress plugins to receive security fixes promptly.

Workarounds

• Restrict access to WordPress admin AJAX endpoints using server-level access controls
• Implement a Web Application Firewall (WAF) with rules to block suspicious requests to the Filter Plus plugin
• Limit user registration and reduce the number of authenticated users who could potentially exploit the vulnerability
• Consider using WordPress security plugins that provide additional capability checks and access logging

# Apache .htaccess workaround to restrict AJAX access by IP (adjust IPs as needed)
<Files admin-ajax.php>
    Order Deny,Allow
    Deny from all
    Allow from 192.168.1.0/24
    Allow from 10.0.0.0/8
</Files>