Both for its simplicity and efficiency to search for the most critical security vulnerabilities that could exist within a web application, a web vulnerability scanner is a popular tool among any company that develops a web application. With the existence of many different scanners that are available to use, one is unlikely the same as the other and the results attained when evaluating these scanners in relation to each other are often not the same. In this thesis, three different open source web vulnerability scanners are evaluated and analysed based on their ability to find SQL injection and cross-site scripting vulnerabilities. The scanners were used on several open source deliberately broken web applications that acted as benchmarks. The benchmarks that caused much diversity in the results from the scanners were further investigated. When analysing the scanners based on the results, both the actual results were analysed on what caused the diversity but most of all the source code of the scanners were explored and investigated. It could be found that the techniques used by the scanners were essentially similar but contained several minor differences that caused the diversity in the results. Most differences were dependant on the variation of the predefined payloads injected by the scanners, but it could also be found that the approaches used to determine if a vulnerability was detected or not could vary as well. The finalised result concluded in a report that reveals and demonstrates the different approaches that any web vulnerability scanner could use and the limitations of them.

The popularity of the internet has made the use of web applications ubiquitous and essential to the daily lives of people, businesses and governments. Web servers and web applications are commonly used to handle tasks and data that can be critical and highly valuable, making them a very attractive target for attackers and a vector for successful attacks that are aimed at the application layer. Existing misuse and anomaly-based detection and prevention techniques fail to cope with the volume and sophistication of new attacks that are continuously appearing, which suggests that there is a need to provide new additional layers of protection. This work aims to design a new layer of defense based on deception that is employed in the context of web application-layer traffic with the purpose of detecting and preventing attacks. The proposed design is composed of five deception strategies: Deceptive Comments, Deceptive Request Parameters, Deceptive Session Cookies, Deceptive Status Codes and Deceptive JavaScript. The strategies were implemented as a software artifact and their performance evaluated in a testing environment using a custom test script, the OWASP ZAP penetration testing tool and two vulnerable web applications. Deceptive Parameter strategy obtained the best security performance results, followed by Deceptive Comments and Deceptive Status Codes. Deceptive Cookies and Deceptive JavaScript got the poorest security performance results since OWASP ZAP was unable to detect and use deceptive elements generated by these strategies. Operational performance results showed that the deception artifact could successfully be implemented and integrated with existing web applications without changing their source code and adding a low operational overhead.