XSS stands for Cross-Site Scripting, and it is a type of security attack where malicious code (often JavaScript) is injected into a webpage, which then runs the code in another user's browser. This gives the attacker the ability to steal data, manipulate the content on the page, or perform other malicious actions, all without the user's knowledge. XSS attacks exploit vulnerabilities in web applications that do not properly validate or filter user input.
How does XSS work?
An XSS attack occurs when an attacker finds a way to inject malicious code into a web application that is displayed to other users. When the code is executed in the user's browser, it can perform actions such as stealing cookies, login credentials, or even taking control of entire accounts.
There are three main types of XSS attacks:
- Reflected XSS: The malicious code is executed immediately in the user's browser when the user clicks a manipulated link or submits a form where input is not properly validated.
- Stored XSS: The malicious code is stored on the server and shown to multiple users over time, e.g., in comments or user profiles, where data is displayed without proper filtering.
- DOM-based XSS: The attack occurs when client-side JavaScript changes the content of the DOM based on malicious user input, without communicating with the server.
Why is XSS dangerous?
XSS attacks are dangerous because they allow attackers to take over the user's browser session and gain access to sensitive information. If a user is logged into a web application such as a bank or an e-commerce platform, a successful XSS attack can give the hacker the opportunity to steal the user's session and obtain unauthorized access to their account.
Some of the biggest risks of XSS include:
- Stealing cookies and session tokens: XSS can be used to steal cookies that contain login credentials and sessions.
- Changing webpage content: Attackers can manipulate the content on webpages, which can deceive users into performing dangerous actions.
- Phishing attacks: Hackers can use XSS to display fake login forms and steal users' credentials.
How to protect against XSS?
Protection against XSS requires that web developers implement security practices that prevent malicious code from being inserted or executed in the user's browser. Here are some ways to protect yourself:
- Input validation: Ensure that all user input is properly validated and filtered before it is displayed on a webpage.
- Escaping output: Make sure to "escape" special characters in user input so they are not executed as code.
- Use Content Security Policy (CSP): A CSP restricts which scripts are allowed to run on a webpage, which can reduce the risk of XSS attacks.
XSS is one of the most common security threats on the web and can have serious consequences, but with the right protective measures, the risk of an attack can be reduced significantly.