CVE-2026-40775: Royal MCP Auth Bypass Vulnerability

CVE-2026-40775 Overview

CVE-2026-40775 is an unauthenticated broken access control vulnerability affecting the Royal MCP WordPress plugin in versions up to and including 1.4.2. The flaw stems from a missing authorization check [CWE-862] that allows unauthenticated attackers to invoke restricted plugin functionality over the network. Because no privileges or user interaction are required, attackers can reach affected endpoints directly from the internet against any WordPress site running a vulnerable version of the plugin.

Critical Impact
Unauthenticated attackers can access protected plugin functions remotely, leading to limited compromise of confidentiality, integrity, and availability of WordPress sites running Royal MCP <= 1.4.2.

Affected Products

Royal MCP WordPress plugin versions <= 1.4.2
WordPress sites with the Royal MCP plugin installed and active
Hosting environments exposing WordPress instances to network access

Discovery Timeline

2026-06-15 - CVE-2026-40775 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-40775

Vulnerability Analysis

The vulnerability is a Broken Access Control issue classified under [CWE-862] Missing Authorization. The Royal MCP plugin exposes one or more functions that should be restricted to authorized users, but the plugin fails to verify the caller's privileges before executing the requested action. Attackers can interact with these functions over HTTP without authenticating to WordPress.

The attack vector is network-based, and exploitation requires neither valid credentials nor user interaction. The impact spans confidentiality, integrity, and availability at a limited level, which aligns with the plugin's restricted operational scope rather than a full site takeover. The EPSS data published on 2026-06-18 indicates a low near-term exploitation probability, but the lack of authentication requirement keeps the practical risk elevated for exposed sites.

Root Cause

The root cause is the absence of capability or nonce verification on plugin endpoints. WordPress plugins should call current_user_can() and check_ajax_referer() or equivalent checks before performing privileged operations. Royal MCP <= 1.4.2 registers handlers that execute without these gates, leaving them reachable by anonymous requests.

Attack Vector

An attacker sends crafted HTTP requests to the plugin's exposed endpoints, such as admin-ajax or REST routes registered by Royal MCP. The server processes the request without enforcing authentication or authorization. The vulnerability is described in the Patchstack Vulnerability Report.

No public proof-of-concept code is available. Refer to the vendor advisory for technical specifics.

Detection Methods for CVE-2026-40775

Indicators of Compromise

Unauthenticated HTTP POST or GET requests to Royal MCP plugin endpoints under /wp-admin/admin-ajax.php or /wp-json/ referencing Royal MCP actions
Unexpected changes to plugin-managed data or settings without a corresponding authenticated administrator session
Access log entries showing high-volume requests targeting plugin paths from unfamiliar IP addresses

Detection Strategies

Monitor WordPress access logs for requests to Royal MCP endpoints originating from unauthenticated sessions
Deploy a Web Application Firewall (WAF) rule set that flags requests to the plugin's actions lacking valid authentication cookies or nonces
Correlate plugin endpoint traffic with subsequent state changes in the WordPress database to identify successful exploitation

Monitoring Recommendations

Enable WordPress audit logging to capture plugin configuration changes and administrative actions
Forward webserver and PHP error logs to a centralized SIEM for correlation across hosts
Alert on anomalous spikes in traffic to /wp-admin/admin-ajax.php with action parameters tied to Royal MCP

How to Mitigate CVE-2026-40775

Immediate Actions Required

Identify all WordPress sites running the Royal MCP plugin and inventory installed versions
Deactivate and remove Royal MCP 1.4.2 or earlier until a patched release is available
Place affected sites behind a WAF with rules restricting access to plugin endpoints
Review WordPress audit logs and database state for signs of prior unauthorized access

Patch Information

No fixed version is referenced in the published advisory data. Monitor the Patchstack Vulnerability Report and the plugin vendor's release notes for a security update beyond version 1.4.2 and apply it as soon as it is published.

Workarounds

Restrict access to /wp-admin/admin-ajax.php and Royal MCP REST routes via IP allowlists at the webserver or WAF layer
Disable the Royal MCP plugin entirely if its functionality is not business-critical
Implement network-level controls that block unauthenticated access to administrative WordPress paths

bash

# Configuration example: Nginx rule to block unauthenticated access to Royal MCP endpoints
location ~* /wp-json/royal-mcp/ {
    allow 10.0.0.0/8;
    deny all;
}

location = /wp-admin/admin-ajax.php {
    if ($arg_action ~* "^royal[_-]mcp") {
        set $block_request 1;
    }
    if ($http_cookie !~* "wordpress_logged_in_") {
        set $block_request "${block_request}1";
    }
    if ($block_request = "11") {
        return 403;
    }
}