What is cross-site request forgery (CSRF), and how can it be mitigated?

Cross-Site Request Forgery (CSRF) is a web security vulnerability where an attacker tricks a user's browser into making an unintentional request to a target website on which the user is authenticated. This can lead to actions being performed on the user's behalf without their consent. CSRF attacks are particularly dangerous when a user is authenticated and has an active session on a targeted site.

Mitigating CSRF involves implementing various preventive measures:

1. Anti-CSRF Tokens: Include unique tokens in each form or request. These tokens are validated on the server side, ensuring that the request is legitimate. Attackers cannot easily forge requests without knowledge of these tokens.

2. SameSite Cookies: Set the SameSite attribute on cookies to control when they are sent with cross-site requests. This attribute helps prevent CSRF attacks by restricting the cookie's scope.

3. Check Referrer Header: Verify the Referrer header on the server side to ensure that requests originate from the same domain. While not foolproof, it adds an additional layer of protection.

4. Use Content Security Policy (CSP): Employ CSP headers to control which domains are allowed to load resources on your website. This helps prevent malicious code injection.

5. Implement Double-Submit Cookies: Embed a random and unique token both in a cookie and as a hidden form field. Upon submission, the server compares both values to validate the request's legitimacy.

6. Employ Same-Origin Policy: This browser security feature restricts web pages from making requests to a different domain than the one that served the web page, reducing the risk of unauthorized cross-site requests.

7. Regularly Update and Patch: Keep web servers, frameworks, and libraries up to date to address known vulnerabilities.

By combining these measures, developers can significantly reduce the risk of CSRF attacks and enhance the overall security of their web applications.