AntiForgery Token in ASP.NET Core - asp.net-core

I am working in a Razor pages project. In ASP.NET Core, #Html.AntiForgeryToken() is applied for preventing cross-site request forgery (XSRF/CSRF) attacks.
And I read an article about it:
https://www.red-gate.com/simple-talk/development/dotnet-development/anti-forgery-validation-asp-net-core/
This defense strategy works just as long as the controller’s code that handles the POST double-checks that it is receiving a hidden field named __RequestVerificationToken and a cookie with the same name.
By using postman, I can just simply copy the cookies value and the antiforgery token, and append it with the request so that I can post without visiting the page. And the cookies and token can be used repeatedly.
My question is, how can I do to prevent users/hackers calling the handlers/controllers without visiting the page and ensure that the token only can be used one time?
Do I have to write my own solutions for this? Or Microsoft already provided a solution?

The antiforgery token prevents csrf attacks. It does this by denying post requests that only contain the cookie. If the attacker has access to the antiforgery token then it is over. This is why the token must change when you log in. And it must be invalidated when you log out. It doesn’t necessarily need to change for each request.
https://owasp.org/www-community/Anti_CRSF_Tokens_ASP-NET

There are many strategies. Microsoft does not recommend you add the token to your cookies collection, but if you do, you must use HTTPS. As you know, cookies are exposed in each request. You can strengthen them with HttpOnly and Secure. But if you add HttpOnly, you can't read it yourself.
A better approach is to use headers because your header won't persist after the request is over.
As for Microsoft, here's a good resource: enter link description here

Related

Is API for CSRF token safe?

Is it safe to build an API to provide CSRF one-time use token to avoid CSRF attack? Will this open a new vulnerability?
I have one more doubt regarding the traditional approach of including CSRF. I wonder that providing the csrf token in the form can be scraped and attack may be implemented by the attacker. Please correct me if my thought process in incorrect.
First of all you need to understand how a CSRF attack looks like. Someone can send you a link to http://malicious.com/whatever.html. You open this site and there will be an invisible form, that will send a POST request to http://example.com/account/1/delete. You will be logged into example.com on some other tab, so assuming the session is handled via a cookie, the cookie gets automatically attached and you execute a request you never intended to and are even unaware of.
We can mitigate the CSRF issue via different means, on of the being anti-CSRF tokens. The idea is that there is some kind of secret malicious.com will be unaware of and that can not easily be guessed. Please note, that in the CSRF scenario your means of attack are making people open some link. You have no access to the content of what they are seeing. You just send them a link and expect some requested to be executed with their access rights.

Why do we need to use the front-channel for an OAuth authorization request?

I've been struggling with this and would love to see if any OAuth experts here have an answer.
For context, I'm trying to integrate OAuth into an existing first-party (internal) front-end client that lives on a subdomain. It's a single-page application. I have an authorization server that has an /oauth2/authorize and oauth2/token endpoint and I'm working with the OAuth 2 with PKCE authorization flow.
In all the examples I've seen externally, it seems like the recommendation is to make a top-level redirect to the authorization URL initial login . And for silently re-authenticating a user (if they were already logged in), using an invisible iFrame set to the authorization URL (and postMessaging the code back to the parent window).
I'm trying to understand what prevents me from making a front-channel request to my /authorize endpoint via Javascript. Something simple like...
const { state, code } = await fetch(authorizationUrl)
For the login case, I can handle a 403 error back from the AS and then redirect them to login from the client-side. For the re-authenticating case (i.e. client has an expired refresh token but is still logged in), this is great because I just get a 200 response and the code back directly in the JSON body and I can use it immediately. There is no top-level redirect, no hassle of saving app state, etc.
It seems like as long as the AS is willing to return the { state, code } via JSON, this should work. This means that
The AS authorize endpoint must be configured to allow CORS on select origins. This seems okay in a first-party context since I know which origins I should allow.
The AS must be sent client credentials (session cookies) with the request (otherwise the AS would have no idea how to determine if the user is logged in). In JS, this would be as simple as adding credentials: true. As long as the cookie credentials have Same-Site: None and the cookie is part of the same domain (cross-domain would not work since some browsers disable cross-site cookie sharing nowadays!)
I feel like I'm missing something crucial here. But at the same time, my prototype is working, so I'd love to get some input from experienced folks here.

Proper way to do jwt refresh tokens with express

I'm thinking of a proper pattern for implementing refresh tokens, but on few steps, I have some questions. I am using nextjs with axios on the frontend and express with cookie-session on the backend.
Here are steps I'm thinking of:
Client sends a log-in request. After logging in I put the access token in the session object and the refresh token into res.cookie, both secure and httpOnly.
// for simplicity options are left out
req.session = { accessToken };
res.cookie("refreshToken", refreshToken)
On every request with axios I supply just the access token. Here's where the first question arises. How would I supply only the access token, without sending the refresh token too, if both are httpOnly?
If the access token is valid do whatever is needed. If not, need to get the refresh token and compare it to a stored one, and so on. Here's the second question. While I understand I need to retrieve the refresh token in this step, how would I do it properly?
Any more advice would be great, thanks.
[EDIT] After some thought I realised that making access token not httpOnly would allow me to send just access token, which would solve my problem. But if that is incorrect please let me know.
Here is the standard pattern - as in this code of mine:
Client sends access token (which may be in an HTTP Only cookie)
When it expires they try to refresh the access token by calling a /refresh endpoint
If the refresh succeeds they retry the API request with the new access token
Otherwise the client redirects the user to sign in again
Don't make the access token non HTTP Only, since any malicious code could then grab it from document.cookie.
This also allows you to set a path of /refresh for the RT cookie, so that it is only sent on refresh requests.
Also ensure that cookies containing tokens are strongly encrypted (AES256) using a symmetric key only known server side. This Express library will do the work for you.

JWT Refresh token and Multi-Page Application

I am going to implement JWT authentication for several independent services.
There will be auth.example.com and service1.example.com, service2.example.com etc.
My assumptions:
JWT can be kept in cookie for ".example.com"
JWT expire time should be small (like 15 mins) because there is no reliable way to logout user with JWT token (revoke token).
Refresh tokens should be used to reissue JWT tokens
Refresh token cookies should be accessible only by auth.example.com for security reasons and because https://www.rfc-editor.org/rfc/rfc6749#section-1.5 says
"Unlike access tokens, refresh tokens are intended for use only with authorization servers and are never sent to resource servers."
Next, if I have a service - multi page application (i.e. not SPA), where some URLs are called "traditional" way, not via Ajax and render HTML
based on some server side logic, which, of course, include checking of user authorization.
then, say, there will be an action service1.example.com/user/showpage
if (user.logged_in) {
render_some_html(get_some_data(user.login))
}
else {
render_anonimous_uses_page()
}
Problem is:
If site user close all site tabs and, then after hour or so, go directly to page /user/showpage (or maybe he
suspend laptop and wake it up in an hour and go to that page).
What if by that time JWT token will expire. Then to refresh it by Refresh token we need to make Ajax call to auth.example.com (because Refresh
token is stored only in auth.example.com cookie) and this is just unaccessible in server side rendering (that pseudocode that I posted above, it's server side, and it's just impossible to make client ajax call in the middle of execution of server code. it's just not applicable here). This way user will be considered logged out
on this stage.
Redirect could be one solution.. but what if site should work for anonymous out users too, and anyway looking for something better.
This problem not exists for SPA application, because before every Ajax call to internal API, it can check JWT and make call to refresh JWT token.
And question is: is this true that JWT in general should not (cannot) be used in Multi-Page (traditional) applications because of this issue? or there is good way to workaround this? or this is not a problem at all (users don't close tabs too often, or they expect site to log them out or redirect etc)?

CSRF Token necessary when using Stateless(= Sessionless) Authentication?

Is it necessary to use CSRF Protection when the application relies on stateless authentication (using something like HMAC)?
Example:
We've got a single page app (otherwise we have to append the token on each link: ....
The user authenticates himself using POST /auth. On successful authentication the server will return some token.
The token will be stored via JavaScript in some variable inside the single page app.
This token will be used to access restricted URLs like /admin.
The token will always be transmitted inside HTTP Headers.
There's NO Http Session, and NO Cookies.
As far as I understand, there should(?!) be no possibility to use cross site attacks, because the browser won't store the token, and hence it cannot automatically send it to the server (that's what would happen when using Cookies/Session).
Am I missing something?
I found some information about CSRF + using no cookies for authentication:
https://auth0.com/blog/2014/01/07/angularjs-authentication-with-cookies-vs-token/
"since you are not relying on cookies, you don't need to protect against cross site requests"
http://angular-tips.com/blog/2014/05/json-web-tokens-introduction/
"If we go down the cookies way, you really need to do CSRF to avoid cross site requests. That is something we can forget when using JWT as you will see."
(JWT = Json Web Token, a Token based authentication for stateless apps)
http://www.jamesward.com/2013/05/13/securing-single-page-apps-and-rest-services
"The easiest way to do authentication without risking CSRF vulnerabilities is to simply avoid using cookies to identify the user"
http://sitr.us/2011/08/26/cookies-are-bad-for-you.html
"The biggest problem with CSRF is that cookies provide absolutely no defense against this type of attack. If you are using cookie authentication you must also employ additional measures to protect against CSRF. The most basic precaution that you can take is to make sure that your application never performs any side-effects in response to GET requests."
There are plenty more pages, which state that you don't need any CSRF protection, if you don't use cookies for authentication. Of course you can still use cookies for everything else, but avoid storing anything like session_id inside it.
If you need to remember the user, there are 2 options:
localStorage: An in-browser key-value store. The stored data will be available even after the user closes the browser window. The data is not accessible by other websites, because every site gets its own storage.
sessionStorage: Also an in browser data store. The difference is: The data gets deleted when the user closes the browser window. But it is still useful, if your webapp consists of multiple pages. So you can do the following:
User logs in, then you store the token in sessionStorage
User clicks a link, which loads a new page (= a real link, and no javascript content-replace)
You can still access the token from sessionStorage
To logout, you can either manually delete the token from sessionStorage or wait for the user to close the browser window, which will clear all stored data.
(for both have a look here: http://www.w3schools.com/html/html5_webstorage.asp )
Are there any official standards for token auth?
JWT (Json Web Token): I think it's still a draft, but it's already used by many people and the concept looks simple and secure. (IETF: https://datatracker.ietf.org/doc/html/draft-ietf-oauth-json-web-token-25 )
There are also libraries for lot's of framework available. Just google for it!
TL;DR
A JWT, if used without Cookies, negates the need for a CSRF token - BUT! by storing JWT in session/localStorage, your expose your JWT and user's identity if your site has an XSS vulnerability (fairly common). It is better to add a csrfToken key to the JWT and store the JWT in a cookie with secure and http-only attributes set.
Read this article with a good description for more info
https://stormpath.com/blog/where-to-store-your-jwts-cookies-vs-html5-web-storage
You can make this CSRF protection stateless by including a xsrfToken JWT claim:
{
"iss": "http://galaxies.com",
"exp": 1300819380,
"scopes": ["explorer", "solar-harvester", "seller"],
"sub": "tom#andromeda.com",
"xsrfToken": "d9b9714c-7ac0-42e0-8696-2dae95dbc33e"
}
So you will need to store the csrfToken in localStorage/sessionStorage as well as in the JWT itself (which is stored in a http-only and secure cookie). Then for csrf protection, verify that the csrf token in the JWT matches the submitted csrf-token header.