CVE-2025-12166 Exploit & Vulnerability Analysis

1. Vulnerability Background

• The flaw is a blind SQL injection in the Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin for WordPress.
• It affects all versions up to and including 1.6.9.9.
• The vulnerability is rooted in two user-controlled parameters: order and append_where_sql.
• An unauthenticated attacker can inject SQL into already-existing queries by supplying malicious values for these parameters.
• This is critical because it allows data extraction from the database without authentication, and can expose sensitive information stored by the WordPress site.

2. Technical Details

Root cause analysis

• The plugin builds SQL queries dynamically in includes/lib/td-util/class-td-db-model.php.
• The order parameter is used to construct an ORDER BY clause.
• The append_where_sql parameter is appended directly to an existing WHERE clause.
• Neither parameter is sufficiently validated or normalized before being concatenated into the SQL string.
• As a result, attacker-controlled input can alter query semantics.

Attack vector and exploitation conditions

• The attacker sends HTTP requests to the plugin endpoint that accepts these parameters.
• Because the plugin does not require authentication for the vulnerable path, the attacker can exploit it remotely.
• Blind SQL injection is possible because the injected payload can modify query execution without returning explicit SQL errors; timing or boolean-based techniques can be used to infer data.

Security implications

• Data confidentiality is at risk: database contents, user records, appointment information, and site configuration can be exposed.
• Depending on database privileges, an attacker may also discover schema details or escalate other attacks.
• Since the vulnerability is unauthenticated, it significantly increases the attack surface.

3. Patch Analysis

What changed

• The patch in includes/lib/td-util/class-td-db-model.php hardens the way dynamic SQL fragments are processed.
• For order, the code now validates and sanitizes the value before it is used in an ORDER BY clause.
• For append_where_sql, the patch prevents raw SQL from being concatenated directly into the WHERE clause, instead using safer construction methods.

How the changes fix the vulnerability

• The original code allowed user input to flow directly into SQL query text.
• The patched code applies context-aware sanitization and/or whitelisting to ensure only valid database identifiers or pre-approved filter expressions are included.
• This prevents attackers from injecting arbitrary SQL fragments and turning the query into a SQL injection vector.

Security improvements introduced

• Removal of raw user-controlled SQL fragment concatenation.
• Introduction of proper escaping/validation for dynamic identifiers.
• More rigorous handling of parameters used in query construction.

4. Proof of Concept Guide

Prerequisites

• WordPress with the vulnerable plugin installed.
• Access to the plugin endpoint that accepts order or append_where_sql.

Step-by-step exploitation

1. Find the request path where the plugin accepts order or append_where_sql parameters.
2. Craft a payload for append_where_sql that injects a conditional expression, for example:
   • append_where_sql=1 AND (SELECT IF(SUBSTRING((SELECT DATABASE()),1,1)='a',SLEEP(5),0))
3. Send the request and measure response time.
4. Vary the condition to infer characters of database values.

Expected behavior

• A normal request returns a valid response quickly.

Exploited behavior

• A malicious request with a time-based payload causes a measurable delay only when the injected condition is true.
• This confirms blind SQL injection.

Verification

• Compare responses with a true condition and a false condition.
• A significant difference in response timing indicates the vulnerability exists.

5. Recommendations

Mitigation strategies

• Upgrade the plugin to the patched version above 1.6.9.9.
• If upgrade is not immediately possible, disable the plugin or block access to the vulnerable endpoints.

Detection methods

• Monitor logs for requests containing order or append_where_sql with unusual SQL fragments.
• Use WAF rules that detect SQL injection patterns in query parameters.
• Audit database queries for unexpected WHERE clause expansions or ORDER BY injections.

Best practices to prevent similar issues

• Never interpolate raw user input into SQL queries.
• Use prepared statements for query parameters.
• For dynamic SQL identifiers like ORDER BY columns, use strict whitelisting or sanitization.
• Treat any parameter that can modify SQL syntax as untrusted and validate it accordingly.