I wonder how does ASP.NET check if an anti-forgery token is valid or not? Like where is ASP.NET storing those tokens? And how are they stored?
The short version is that a generated token is stored in 2 places: (a) cookie (b) hidden form value. When the form is submitted, these 2 values are compared against each other to determine if they are valid. For further reading:
http://www.asp.net/web-api/overview/security/preventing-cross-site-request-forgery-(csrf)-attacks
http://www.codeproject.com/Articles/793384/ASP-NET-Anti-Forgery-Tokens-internals
A stepwise explanation that is more clear than the accepted answer imho (from https://learn.microsoft.com/en-us/aspnet/web-api/overview/security/preventing-cross-site-request-forgery-csrf-attacks)
The client requests an HTML page that contains a form.
The server includes two tokens in the response. One token is sent as a cookie. The other is placed in a hidden form field. The tokens are generated randomly so that an adversary cannot guess the values.
When the client submits the form, it must send both tokens back to the server. The client sends the cookie token as a cookie, and it sends the form token inside the form data. (A browser client automatically does this when the user submits the form.)
If a request does not include both tokens, the server disallows the request.
The above description is not all what is done, in case of AjaxRequest the antiforgery, specifically in get requests, will not usually send the Form with the hidden value for comparison, instead you will need to set a header value with the same content of the cookie via javascript.. the header name that you should set is by default X-XRF-Token header [related to angularjs] ... of course you will need to disable CORS or enable it for only specific domains to protect the APIs, SAMEORIGIN also need to be set to avoid clickjacking ..
Related
I am Looking at the Network activity of this page: https://helm.csod.com/ux/ats/careersite/4/home?c=helm&lang=de-DE.
Specifically at the post request with the Name: "search". Its using an authorization token.
tldr: How is the following authorization token stored on the Client side?
Goal:
I would like to understand how the browser (client-side) stores this authorization token. I dont Need to get the data or know how to scrape with selenium or sthg. I would just be interested in the mechanics behind.
What i tried:
I find the token in the page source: view-source:https://helm.csod.com/ux/ats/careersite/4/home?c=helm&lang=de-DE.
It seems like there is an object csod created in /player-career-site/1.15.4/pages/home.js.
then the key is stored in csod.context.
Finally, csod.player.initialize(csod.context) is called.
Unfortunately, i failed digging in the Code and finding These function as there where too many Matches for initialize and my js are skills too bad.
As storage i am only Aware of the Cookies. It might be transformed / encrypted and stored in the cookies? But how is it then restored to the "original" token, before being added to the request Header?
This seems to be a CSRF prevent method.
The token is created with a key in the back end, it stores the original key in a session and sends the token to the client side.
When the client sends a request, the token is posted with the data as a header or with the data, then the back end gets the stored key in the session, generate the token with the same method and compare it with the posted token. If they are equal there is no problem, access granted.
It is not necessary to restore as you can't decrypt that depending on the algorithm (sha256, md5, etc)
And the browser don't do that, as it can be manipulated, there is no sense to.
The token sent here is JWT(JSON Web Token). This is a widely used standard authentication mechanism.
You can create your own token in any languages like JS, Java, PHP, Python, etc.
I am adding a basic authentication flow:
Let's say a user comes on a form. Enter his email & password.
Now an HTTP request is being sent to the server with credentials. The backend server checks the details and if successful, then returns a response containing the authentication token.
Most of the time this token is stored in localstorage and sometimes in cookies.
Now for every request the token is picked from the stored location and sent in the header.
On the backend, it is checked if the request header has the details or not. And then respond accordingly.
At last, whenever someone logs out then that token is removed from the front end.
I hope it helps! Let me know if you have any queries
I still don't understand how the Anti-forgery Token works in MVC.
From the MSDN.
Anti-Forgery Tokens
To help prevent CSRF attacks, ASP.NET MVC uses anti-forgery tokens, also called request verification tokens.
The client requests an HTML page that contains a form.
The server includes two tokens in the response. One token is sent as a cookie. The other is placed in a hidden form field. The tokens are generated randomly so that an adversary cannot guess the values.
When the client submits the form, it must send both tokens back to the server. The client sends the cookie token as a cookie, and it sends the form token inside the form data. (A browser client automatically does this when the user submits the form.)
If a request does not include both tokens, the server disallows the request.
Here is an example of an HTML form with a hidden form token:
<form action="/Home/Test" method="post">
<input name="__RequestVerificationToken" type="hidden"
value="6fGBtLZmVBZ59oUad1Fr33BuPxANKY9q3Srr5y[...]" />
<input type="submit" value="Submit" />
My question is that since we can find the hidden token value easily by looking the source code (F12 in any browser). Then can we manually set the cookie by going to the Developer Tools (Ctrl-Shift-J or Tools -> Developer Tools) -> Console and the you can enter javascript command:
document.cookie="keyofcookie=valueofcookie"?
Then we cam manually set the tokens same therefore to disable Anti Forgery technology?
That cookie is HttpOnly and it cannot be set from javascript since all latest browsers implement HttpOnly. Also, both cookie token and form token contain different base 64 encrypted information. Decryption will be server side stuff.
Moreso, These tokens are not compared for equality. They complement each other for data. Also, you did not read the complete article. MVC has its own methods to validate token as well..
Check if the link below helps.
https://www.codeproject.com/Articles/793384/ASP-NET-Anti-Forgery-Tokens-internals
As the documentation says:
Anti-forgery tokens work because the malicious page cannot read the
user's tokens, due to same-origin policies. (Same-origin policies
prevent documents hosted on two different sites from accessing each
other's content. So in the earlier example, the malicious page can
send requests to example.com, but it cannot read the response.)
That means, copying the cookie value and using it to any different location will not work because of the said policy.
I have implemented basic aunthentation from url http://www.asp.net/web-api/overview/security/basic-authentication. Now I have a question that how i send the basic aunthentation to user on login or on register action that is inside controller.
in short how i create a token and integrated in responsed header.
Kindly help me i have spent more then 4 hours on it.
Thanks
The token is created manually from the credentials users provide.
This means that you have to show a login form in your ios application, gather the username and password and then append the authentication header to each request.
The name of the header is Authorization.
The value is computed as follows. You take the username + ':' + password and encode such string to a byte array. Then you get base64 out of the array.
The value of the header is basic [base64ofusernamepassword] where the [base64ofusernameandpassword] is replaced by the base64 of the username and password you just computed previously.
The exact way of appending custom headers to requests can vary depending on the client technology but it should be easy, no matter which technology is used.
How AntiForgeryToken gets invalidated? I have set up this token to prevent CSRF attacks on my login page and have inspected it with fiddler. When i call GET method the token generates as hidden field __RequestVerificationToken. When i post login data should this token be changed on next GET call? I catch with fiddler this value with post data and reissue/replay request and this works. Is this good behavior, or this replay should not happen because token value should not be valid after i leave that form.
Thanks in advance.
The token is tied to a session cookie; when the session goes away and the cookie disappears the token will be rendered invalid. The reason replays work in Fiddler is that Fiddler is capturing (and replaying) both the session cookie and the form token.
You could simulate session expiration by removing the request's Cookie header from within Fiddler before replaying. The server should then reject the form's __RequestVerificationToken field.
I have an asp.net login page, which when initialized sets some session variables. When the user clicks login, an AJAX request is made which validates the user and sets additional session variables and returns a result to the client. The client is then redirected based on the login result. In the redirected page, I can access the session variables set when the login page was initialized (i.e. before the login) but none are present for those set during the login validation (part of an ajax call).
is this expected behaviour? Why would an ajax call generate a new session and thus cause the data to be lost?
Thanks
Is the location for your ajax call in the same application space as the rest of the application?? If I remember right you can't share session information between applications. That may be what's going on.
Normally the browser sends the sends the session id along with ajax requests. If you use Firebug or something similar you can view the contents of the ajax request and check if the session id is sent along.
The session id is stored in a cookie, which (depending on options) can only be used for the same domain/host name. This could be a reason why it is not sent.
Depending on your code, I guess that if no session id was sent a new one is created.
The session id is stored in a cookie, which is returned in the header of the response. As you are doing an AJAX call, the cookie is just part of the response. If you want to use the same session for another request, you have to get that cookie and send it along in the header of the request.