CVE-2025-12166: WordPress Appointment Plugin SQLi Flaw

CVE-2025-12166 Overview

The Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress contains a blind SQL Injection vulnerability in all versions up to and including 1.6.9.9. The vulnerability exists due to insufficient escaping on user-supplied parameters and a lack of sufficient preparation on existing SQL queries. This security flaw affects the order and append_where_sql parameters, allowing attackers to manipulate database queries without authentication.

Critical Impact

Unauthenticated attackers can append additional SQL queries into already existing queries, enabling extraction of sensitive information from the WordPress database including user credentials, personal data, and other confidential information.

Affected Products

• Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress versions up to and including 1.6.9.9
• WordPress installations running vulnerable versions of the plugin
• Any website utilizing the Simply Schedule Appointments functionality

Discovery Timeline

• 2026-01-14 - CVE CVE-2025-12166 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2025-12166

Vulnerability Analysis

This blind SQL Injection vulnerability (CWE-89) occurs because the plugin fails to properly sanitize and escape user-supplied input before incorporating it into SQL queries. The affected parameters, order and append_where_sql, are directly used in database operations without adequate security controls.

Blind SQL Injection is particularly dangerous because attackers can infer database contents through the application's responses or timing differences, even when error messages are suppressed. In this case, the vulnerability enables unauthenticated attackers to extract sensitive information systematically from the WordPress database.

Root Cause

The root cause is insufficient input validation and improper use of prepared statements in the plugin's database query construction. Specifically:

1. The order parameter allows manipulation of the ORDER BY clause in SQL queries
2. The append_where_sql parameter permits injection of arbitrary WHERE clause conditions
3. Both parameters lack proper escaping and parameterization before being concatenated into SQL statements

WordPress provides functions like $wpdb->prepare() for safely constructing SQL queries, but these were not properly implemented for the vulnerable parameters.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can craft malicious HTTP requests containing SQL injection payloads in the order or append_where_sql parameters. Since this is a blind SQL injection, attackers typically use time-based or boolean-based techniques to extract data character by character.

For example, an attacker could leverage time-based blind SQL injection by injecting payloads that cause conditional delays, inferring database contents based on response timing. The vulnerability allows extraction of sensitive database information including WordPress user tables, plugin configurations, and any custom data stored by the appointment system.

For detailed technical analysis, refer to the Wordfence Vulnerability Report.

Detection Methods for CVE-2025-12166

Indicators of Compromise

• Unusual database query patterns in WordPress logs containing order or append_where_sql parameters with SQL syntax
• Web access logs showing repeated requests with varying payloads to appointment-related endpoints
• Unexpected time delays in page responses potentially indicating time-based blind SQL injection attempts
• Database access patterns showing sequential extraction of table contents

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect SQL injection patterns in request parameters
• Enable WordPress database query logging and monitor for anomalous query structures
• Configure intrusion detection systems to alert on classic SQL injection signatures including UNION, SLEEP, BENCHMARK, and conditional operators
• Review web server logs for high-frequency requests to the plugin's AJAX endpoints

Monitoring Recommendations

• Monitor all incoming requests to the Simply Schedule Appointments plugin endpoints for SQL injection indicators
• Set up alerts for unusual database query execution times that may indicate time-based blind injection
• Track failed database queries or syntax errors that could indicate active exploitation attempts
• Implement rate limiting on appointment booking endpoints to slow potential automated exploitation

How to Mitigate CVE-2025-12166

Immediate Actions Required

• Update the Simply Schedule Appointments Booking Plugin to a version newer than 1.6.9.9 immediately
• Audit WordPress database logs for any signs of prior exploitation
• Consider temporarily disabling the plugin if an update is not immediately available
• Implement WAF rules to block SQL injection attempts targeting known vulnerable parameters

Patch Information

The vulnerability has been addressed in versions beyond 1.6.9.9. The fix implements proper input sanitization and prepared statement usage for the order and append_where_sql parameters. Technical details of the patch can be reviewed in the WordPress Changeset Update.

Site administrators should:

1. Navigate to the WordPress admin dashboard
2. Go to Plugins → Installed Plugins
3. Update the Simply Schedule Appointments plugin to the latest available version
4. Verify the plugin version is newer than 1.6.9.9

Workarounds

• Deploy a Web Application Firewall with SQL injection protection rules enabled
• Restrict access to the appointment booking functionality to authenticated users only if possible
• Implement server-level input validation for the order and append_where_sql parameters
• Consider using WordPress security plugins that provide real-time SQL injection protection

# Example: Block suspicious requests at the web server level (Apache .htaccess)
# Add to WordPress root .htaccess file
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{QUERY_STRING} (order|append_where_sql)=.*(%27|'|%22|"|union|select|concat|benchmark|sleep) [NC]
RewriteRule .* - [F,L]
</IfModule>