XSS (Cross-Site Scripting) is a malicious attack where an attacker injects harmful JavaScript code into a web page. When a user visits the page, the embedded JavaScript executes, allowing the attacker to target the user with malicious actions.
A common form of XSS attack is cookie theft. Websites often use cookies to identify users. If an attacker can execute JavaScript on a page, they can read and steal the user’s cookies. Once the attacker has access to the cookies, they can impersonate the user and log in to the website.
There are three primary ways to mitigate XSS attacks:
- Filtering User Input: Implement a “whitelist” approach to filter out potentially dangerous HTML tags and attributes. Only allow the tags and attributes deemed safe to be sent to the server, blocking everything else. This method helps prevent various forms of XSS attacks.
- Special Handling of Data: Use methods like PHP’s
htmlspecialchars()to escape potentially harmful characters when rendering data on the webpage, ensuring that JavaScript code is not executed. - Content Security Policy (CSP): Implementing a Content Security Policy (CSP) can help prevent XSS attacks by specifying trusted sources for content, restricting the execution of untrusted scripts.