A description and analysis of the vulnerabilities caused by programming errors in Web applications, this book is written from both from the attacker's and security specialist's perspective. Covered is detecting, investigating, exploiting, and eliminating vulnerabilities in Web applications as well as errors such as PHP source code injection, SQL injection, and XSS. The most common vulnerabilities in PHP and Perl scripts and methods of exploiting these weaknesses are described, information on writing intersite scripts and secure systems for the hosted sites, creating secure authorization systems, and bypassing authorization. Uncovered is how attackers can benefit from the hosted target and why an apparently normal-working application might be vulnerable.