April 2026
Intermediate
1009 pages
34h 15m
English
Content preview from PHP and MySQL
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32.2 XSS
One term that frequently appears in the recurring horror stories about websites with security vulnerabilities is cross-site scripting. This should actually be abbreviated to CSS, but this acronym is already reserved for Cascading Style Sheets, so the "X" was chosen, which often stands for cross, as it does here.
The effect of XSS is that script code is injected into the current page from outside. This crosses an authorization barrier because you can fool a website into believing that the injected code is your own. A small example will illustrate this. Imagine a simple guestbook application, as you have seen often in this book. In the following listing, you can first see the (lousy) script for entering data into the guestbook database ...
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