The paper proposes a security testing technique to detect known vulnerabilities of web applications using both static and dynamic analysis. We also present a process to improve the security of web applications by mitigating many of the vulnerabilities revealed in the testing phase, and address a new method for detecting unknown vulnerabilities by applying dynamic black-box testing based on a fuzzing technique. The fuzzing technique includes a structured fuzzing strategy that considers the input data format as well as misuse case generation to enhance the detection rate compared to general fuzzing techniques.