CSRF (Cross-Site Request Forgery) is a web security vulnerability that allows an attacker to exploit the trust between a user's browser and a web application. It occurs when a malicious website or application tricks a victim into performing an unwanted action on another website where the victim is authenticated.
CSRF attacks take advantage of the fact that many websites rely solely on session cookies or other forms of authentication to identify a user's identity and permissions. By exploiting this trust, an attacker can trick the victim into unknowingly performing actions on their behalf, such as changing account settings, making financial transactions, or submitting forms.
Here's an example to illustrate how a CSRF attack works:
Suppose there is a vulnerable web application that allows users to change their email address by sending a POST request to the server:
```
<form action="
https://example.com/account/update_email" method="POST">
<input type="hidden" name="email" value="
attacker@example.com">
<input type="submit" value="Update Email">
</form>
```
If a victim, who is logged into the vulnerable web application, visits a malicious website controlled by an attacker, the attacker could include the following code on their page:
```
<img src="
https://example.com/account/update_email"
width="0" height="0" style="display:none"
onload="document.forms[0].submit()">
```
When the victim loads the attacker's page, the hidden form is automatically submitted in the background without the victim's knowledge. The browser sends a request to the vulnerable web application, updating the victim's email address to the one specified by the attacker.
To prevent CSRF attacks, web developers can implement the following measures:
1. Use Anti-CSRF Tokens: Include a unique token in each HTML form or AJAX request that requires a user's authentication. This token is validated on the server-side to ensure that the request originated from the same site and the user who initiated it.
2. Implement Same-Site Cookies: Set the "SameSite" attribute on session cookies to restrict their scope to the same origin. This prevents the browser from automatically including cookies in cross-site requests.
3. Implement Cross-Origin Resource Sharing (CORS): Configure servers to include appropriate CORS headers to restrict cross-origin requests and specify which origins are allowed to access specific resources.
4. Require Re-authentication for Sensitive Actions: For critical actions such as changing passwords or making financial transactions, request the user to provide additional authentication, such as re-entering their password.
5. Educate Users: Raise awareness among users about the risks of clicking on suspicious links or opening untrusted websites.
It is essential for web developers to be aware of CSRF vulnerabilities and follow secure coding practices to mitigate this type of attack. Regular security testing, including vulnerability scanning and penetration testing, can help identify and address potential CSRF vulnerabilities in web applications.
