CVE-2025-11723: WordPress Simply Schedule Appointments Plugin

CVE-2025-11723 Overview

The Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 1.6.9.5 via the hash() function due to use of a hardcoded fall-back salt. This makes it possible for unauthenticated attackers to generate a valid token across sites running the plugin that have not manually set a salt in the wp-config.php file and access booking information that will allow them to make modifications.

Critical Impact

Unauthenticated attackers can exploit the hardcoded fallback salt to generate valid authentication tokens, gaining unauthorized access to booking information and the ability to modify appointment data across vulnerable WordPress installations.

Affected Products

• Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress versions up to and including 1.6.9.5
• WordPress installations using the plugin without a manually configured salt in wp-config.php
• All sites running vulnerable versions with default salt configuration

Discovery Timeline

• 2026-01-06 - CVE CVE-2025-11723 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-11723

Vulnerability Analysis

This vulnerability stems from a cryptographic weakness classified as CWE-330 (Use of Insufficiently Random Values). The Simply Schedule Appointments plugin implements a hash() function for generating authentication tokens used to access and modify booking information. When a WordPress site administrator has not explicitly configured a custom salt value in the wp-config.php file, the plugin falls back to using a hardcoded salt value embedded in the source code.

Since this fallback salt is identical across all installations using the vulnerable plugin versions, an attacker can predict and generate valid tokens without any authentication. This allows for unauthorized access to sensitive booking data and enables modification of appointment records.

The network-accessible nature of this vulnerability means remote attackers can exploit it without requiring any prior authentication or user interaction.

Root Cause

The root cause is the use of a hardcoded cryptographic salt as a fallback mechanism in the token generation process. When the plugin's hash() function is invoked and no custom salt has been defined in wp-config.php, it defaults to a static, predictable value that is identical across all vulnerable installations. This design flaw violates fundamental cryptographic principles requiring unique, random secrets for token generation.

Attack Vector

The attack exploits the predictable nature of the hardcoded fallback salt through the following mechanism:

1. An attacker identifies a WordPress site using the Simply Schedule Appointments plugin
2. The attacker reverse-engineers or extracts the hardcoded fallback salt from the plugin source code
3. Using the known salt, the attacker generates valid authentication tokens
4. These tokens grant access to the booking management endpoints without authentication
5. The attacker can then view, modify, or delete appointment booking data

Since no real code examples are available, the vulnerability mechanism can be understood as follows: The plugin's hash() function uses a hardcoded string as a fallback salt when generating tokens. This predictable value allows attackers to craft valid tokens for accessing protected booking endpoints. For detailed technical information, refer to the WordPress Plugin Change Log and the Wordfence Vulnerability Report.

Detection Methods for CVE-2025-11723

Indicators of Compromise

• Unexpected modifications to booking records without corresponding admin activity logs
• Unusual API requests to booking management endpoints from unknown IP addresses
• Token-based authentication attempts that bypass normal WordPress user authentication
• Multiple booking queries or modifications from unrecognized sources

Detection Strategies

• Monitor web server access logs for suspicious requests to plugin endpoints containing authentication tokens
• Implement anomaly detection for booking modification patterns that don't correlate with legitimate admin sessions
• Review WordPress activity logs for booking changes occurring outside normal business hours or from unknown locations
• Deploy web application firewall (WAF) rules to detect and block token enumeration attempts

Monitoring Recommendations

• Enable detailed logging for all booking plugin API interactions
• Set up alerts for bulk booking data access or modifications
• Monitor for requests from IP addresses associated with known vulnerability scanners
• Track authentication token usage patterns to identify potential abuse

How to Mitigate CVE-2025-11723

Immediate Actions Required

• Update the Simply Schedule Appointments plugin to a version newer than 1.6.9.5
• Configure a unique, cryptographically secure salt in your wp-config.php file immediately
• Audit recent booking modifications to identify any unauthorized changes
• Review access logs for suspicious token-based authentication attempts

Patch Information

The vulnerability has been addressed in plugin updates released after version 1.6.9.5. Administrators should update to the latest available version through the WordPress plugin repository. The fix details can be reviewed in the WordPress Plugin Change Log. Additional vulnerability context is available via the Wordfence Vulnerability Report.

Workarounds

• Add a custom salt definition to your wp-config.php file to override the hardcoded fallback
• Implement additional access controls at the web server level to restrict booking endpoint access
• Consider temporarily disabling the plugin until it can be updated if immediate patching is not possible
• Use a web application firewall to filter suspicious requests to plugin endpoints

# Configuration example - Add to wp-config.php
# Generate a unique salt using a secure random generator
define('SSA_BOOKING_SALT', 'your-unique-cryptographically-secure-random-string-here');

# Alternatively, restrict access to booking endpoints via .htaccess
# Add to your WordPress .htaccess file
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_URI} ^/wp-json/ssa/
    RewriteCond %{HTTP:X-Authorized-Source} !^your-secret-header$
    RewriteRule ^ - [F,L]
</IfModule>