The MasterStudy LMS WordPress Plugin for Online Courses and Education plugin for WordPress is vulnerable to Time-based Blind SQL Injection via the 'order' and 'orderby' parameters in the /lms/stm-lms/order/items REST API endpoint in versions up to and including 3.7.25. This is due to insufficient input sanitization combined with a design flaw in the custom Query builder class that allows unquoted SQL injection in ORDER BY clauses. When the Query builder detects parentheses in the sort_by parameter, it treats the value as a SQL function and directly concatenates it into the ORDER BY clause without any quoting. While esc_sql() is applied to escape quotes and backslashes, this cannot prevent ORDER BY injection when the values themselves are not wrapped in quotes in the resulting SQL statement. This makes it possible for authenticated attackers, with subscriber-level access and above, to append arbitrary SQL queries via the ORDER BY clause to extract sensitive information from the database including user credentials, session tokens, and other confidential data through time-based blind SQL injection techniques.