Abstract
Today, with the changes and developments in software technologies, web applications have gained an important place by being actively used in many sectors. Due to the fact that web applications do not require installation costs and are easily accessible and operable, the increased usage rate in recent years makes these systems the target of cyber hackers. As a result of cyber attacks, services are blocked, and material and moral damages and data privacy violations are experienced. Within the scope of this study, web applications are explained, vulnerabilities that threaten software security and the measures that can be taken against these vulnerabilities are included. Particularly, security threats to web applications, security principles, secure software development lifecycles, test tools, and hardware and software products used for security are examined. In addition, SAMM and BSIMM models, which are maturity models used in secure software development, are discussed.