What is Cross-Site Scripting (XSS)?

Cross-site scripting (XSS) is a type of attack in which an attacker injects malicious scripts into an otherwise harmless and trustworthy website. These malicious scripts are then unknowingly executed by other visitors to the website, making it vulnerable to further attacks, such as identity theft or the leaking of sensitive information.

What types of cross-site scripting are there?

There are different types of cross-site scripting attacks:

1. Reflected XSS: In a reflected XSS attack, malicious scripts are inserted into a URL or form field and sent to the server. The server then returns the injected scripts as part of the response and they are executed by the victim's browser.
2. Stored XSS: In a stored XSS attack, malicious scripts are stored on the server, e.g. in a database or a forum post. When a user visits the page where the malicious scripts are stored, they are sent from the server to the user's browser and executed.
3. DOM-based XSS: In a DOM-based XSS attack, malicious scripts are executed directly in the victim's browser without being sent to the server. This is done by modifying the victim's URL or by other client-side manipulations.

How can you protect yourself against cross-site scripting?

Various security measures can be taken to protect against XSS attacks:

1. Input Validation: the web application should validate all user input and ensure that it matches the expected formats and parameters. This can help prevent the introduction of malicious code.
2. Output Encoding: All output sent from the web application to the user should be correctly encoded to prevent malicious scripts from being executed in the user's browser. This can be achieved by using frameworks or libraries that provide automatic output encoding.
3. Content Security Policy (CSP): By implementing a content security policy, it is possible to determine which resources may and may not be loaded from a website. This can help to reduce the risk of XSS attacks by restricting access to external scripts and resources.

By implementing these security measures, web applications can be effectively protected from XSS attacks, ensuring the security and integrity of the application and user data.