CSRF Token comparison fails with Spring Security 6

Understanding CSRF Token Comparison Failures in Spring Security 6

Cross-Site Request Forgery (CSRF) is a type of attack that tricks a user's browser into submitting a request to a web application that the user did not intend to make. Spring Security provides protection against CSRF attacks by generating a CSRF token for each user and requiring that this token be included in all requests that modify data.

In Spring Security 6, the XorCsrfTokenRequestAttributeHandler is the default handler for CSRF tokens. This handler is responsible for decoding the CSRF token from the request and comparing it to the token stored in the user's session. If the tokens do not match, the request is rejected.

However, some users have reported that the XorCsrfTokenRequestAttributeHandler is not decoding the CSRF token from the request header correctly. This can lead to CSRF token comparison failures, even when the token is being sent in the correct header.

One possible solution to this issue is to use the CsrfTokenRequestAttributeHandler instead of the XorCsrfTokenRequestAttributeHandler. The CsrfTokenRequestAttributeHandler is the previous default handler in Spring Security 5.x and it does not have the same issue with decoding the CSRF token from the request header.

Another possible solution is to use the /csrf endpoint to retrieve the CSRF token. This endpoint returns the CSRF token in a JSON response, which can then be used by the JavaScript client to set the CSRF token header on all requests.

Why does Spring Security return the XSRF-TOKEN cookie to the browser?

Spring Security returns the XSRF-TOKEN cookie to the browser so that the browser can automatically send the CSRF token with all requests. This is more convenient for the user, as they do not have to manually set the CSRF token header on each request.

However, if you are using the /csrf endpoint to retrieve the CSRF token, you do not need to return the XSRF-TOKEN cookie to the browser. This is because the JavaScript client can retrieve the CSRF token from the /csrf endpoint and set the CSRF token header on all requests without the need for a cookie.

Code Example:

@GetMapping("/csrf")
public CsrfToken csrfToken(CsrfToken csrfToken) {
    return csrfToken;
}

This endpoint returns the CSRF token in a JSON response, which can then be used by the JavaScript client to set the CSRF token header on all requests.

Conclusion CSRF token comparison failures can be a frustrating issue, but they can be resolved by using the correct CSRF token handler or by using the /csrf endpoint to retrieve the CSRF token. Once you have resolved the issue, you can be confident that your application is protected from CSRF attacks.