Cross-Site Scripting (XSS)
Definition
Cross-Site Scripting (XSS) is a type of security vulnerability typically found in web applications. XSS attacks enable attackers to inject client-side scripts into web pages viewed by other users. A cross-site scripting vulnerability may be used by attackers to bypass access controls such as the same-origin policy.
Why It Matters
XSS attacks can be used to steal user session cookies, deface websites, or redirect users to malicious sites. The attack executes in the victim's browser, and the browser trusts the script because it appears to come from the legitimate website.
Contextual Example
A website has a comment section that doesn't properly sanitize user input. An attacker posts a comment containing a malicious `<script>` tag. When other users view the comment, the script executes in their browser, potentially stealing their session cookie and sending it to the attacker.
Common Misunderstandings
- The key to preventing XSS is proper input validation and output encoding. Any data that comes from a user should be treated as untrusted and properly sanitized before being displayed on a page.
- There are different types of XSS, including Stored XSS, Reflected XSS, and DOM-based XSS.