CVE-2025-39541: WP Simple Booking Calendar Auth Bypass Flaw

CVE-2025-39541 Overview

CVE-2025-39541 is a Missing Authorization vulnerability [CWE-862] affecting the Roland Murg WP Simple Booking Calendar plugin for WordPress. The flaw impacts all plugin versions up to and including 2.0.13. An authenticated attacker with low privileges can access functionality that should require higher-level authorization. The vulnerability results from broken access control on plugin actions, allowing unauthorized users to interact with calendar data they should not be able to reach.

Critical Impact

Authenticated low-privilege users can bypass authorization checks in the WP Simple Booking Calendar plugin, leading to unauthorized access to booking calendar data on affected WordPress sites.

Affected Products

• Roland Murg WP Simple Booking Calendar plugin for WordPress
• All versions from initial release through 2.0.13
• WordPress sites with the wp-simple-booking-calendar plugin installed

Discovery Timeline

• 2025-09-09 - CVE-2025-39541 published to the National Vulnerability Database (NVD)
• 2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-39541

Vulnerability Analysis

The vulnerability stems from missing authorization checks within the WP Simple Booking Calendar plugin. The plugin exposes actions that do not properly verify whether the requesting user holds the required capability for the operation. As a result, a user authenticated with a low-privilege role (such as Subscriber) can invoke functionality intended for administrators or editors. The impact is limited to confidentiality, with no direct integrity or availability effects reported in the advisory.

Root Cause

The root cause is a Broken Access Control condition classified under CWE-862: Missing Authorization. Plugin request handlers do not perform capability checks using WordPress functions such as current_user_can() before executing sensitive operations. Any authenticated session with minimal privileges therefore satisfies the implicit access requirement.

Attack Vector

Exploitation requires network access to the target WordPress site and a valid authenticated account with low privileges. No user interaction is required. An attacker submits crafted requests to plugin endpoints exposed through admin-ajax.php or plugin-registered actions. The affected handlers process the request without verifying whether the caller has the required role, returning data or performing actions that should be restricted. See the Patchstack Vulnerability Report for advisory details.

Detection Methods for CVE-2025-39541

Indicators of Compromise

• Unexpected requests from low-privilege authenticated users to wp-admin/admin-ajax.php referencing WP Simple Booking Calendar actions
• WordPress access logs showing repeated plugin action calls originating from Subscriber-level or newly registered accounts
• Outbound scraping patterns targeting booking calendar endpoints on the site

Detection Strategies

• Audit installed WordPress plugins and flag any instance of wp-simple-booking-calendar at version 2.0.13 or earlier
• Review web server access logs for HTTP POST or GET requests to plugin-registered AJAX actions from non-administrator accounts
• Correlate authentication events with plugin action invocations to identify low-privilege accounts accessing restricted functionality

Monitoring Recommendations

• Enable WordPress activity logging to capture plugin action calls and the associated user role
• Alert on new Subscriber-role account registrations followed by requests to plugin admin actions
• Monitor for anomalous access patterns to /wp-admin/admin-ajax.php with plugin-specific action parameters

How to Mitigate CVE-2025-39541

Immediate Actions Required

• Update the WP Simple Booking Calendar plugin to a version later than 2.0.13 as soon as a patched release is available
• Disable the plugin on affected WordPress installations if a patched version is not yet installed
• Audit user accounts and remove or suspend unrecognized low-privilege accounts
• Review site registration settings and disable open user registration if it is not required

Patch Information

At the time of NVD publication, the advisory lists all versions up to and including 2.0.13 as affected. Site owners should monitor the Patchstack advisory and the plugin's WordPress.org page for a fixed release, then apply the update promptly.

Workarounds

• Restrict access to /wp-admin/ and admin-ajax.php at the web server or Web Application Firewall (WAF) layer for untrusted networks
• Deploy a virtual patch through a WordPress security plugin or WAF ruleset that blocks unauthorized calls to wp-simple-booking-calendar actions
• Enforce the principle of least privilege by removing unused user accounts and limiting role assignments

# Example: temporarily disable the vulnerable plugin via WP-CLI
wp plugin deactivate wp-simple-booking-calendar

# Verify the plugin status
wp plugin status wp-simple-booking-calendar