With the recent rapid increase in interactive web appli- cations that employ back-end database services, an SQL in- jection attack has become one of the most serious security threats. The SQL injection attack allows an attacker to ac- cess the underlying database, execute arbitrary commands at intent, and receive a dynamically generated output, such as HTML web pages. In this paper, we present our tech- nique, Sania, for detecting SQL injection vulnerabilities in web applications during the development and debugging phases. Sania intercepts the SQL queries between a web application and a database, and automatically generates elaborate attacks according to the syntax and semantics of the potentially vulnerable spots in the SQL queries. In ad- dition, Sania compares the parse trees of the intended SQL query and those resulting after an attack to assess the safety of these spots. We evaluated our technique using real-world web applications and found that our solution is efficient in comparison with a popular web application vulnerabilities scanner. We also found vulnerability in a product that was just about to be released.