In the OAuth2 authorization grant flow, the client application passes a state parameter to the authorize endpoint. When the state parameter is visible in the browser url, how does state parameter prevent CSRF attacks.
Related
I have a confusion on, whether the redirect_uri in OAUTH authorization grant type, a html page or an API call?
The redirect_uri in OAuth2 is the endpoint where the client receives the authorization code (authorization code) or access token (implicit grant).
The authorization server typically redirects the user's browser back to the client via an HTTP 302 redirect status code.
However, Openid Connect defines a response_mode=form_post, which makes the authorization server return a HTML page with a form containing the parameters as (hidden) fields that is auto-submitted to the client application.
How does the redirect in OAuth with IdentityServer4 work in detail? Calls the identity server the redirect URL directly (in case of loopback likely not possible) or does the browser get a response from Identity server with the redirect as parameter and the Browser does the redirect?
Is there a known issue that the response of the identity server can be changed to redirect to an other site? So can steal the authentication code.
IdentityServer4 redirects in the browser.
Yes, there is a known issue that response of identity server can be changed to redirect to an other site. There are also ways to mitigate those risks. You can use PKCE and nonce.
https://auth0.com/docs/flows/concepts/auth-code-pkce
https://developer.okta.com/blog/2019/08/22/okta-authjs-pkce
Rather than redirecting to another to a malicious endpoint (which will expose authorization code), higher probability is to have a Cross-site request forgery (CSRF) attack. For this OAuth 2.0 spec provide you with state parameter (more on this).
Regarding possibility of redirecting to a malicious endpoint, for this to be done,
Your original request must contain redirect url of malicious endpoit
Identity server must validate this url and then decide to perform the redirect
The second point is difficult to exploit (but possible). Because from OAuth 2.0 definition you register redirect URL when you register your client
The authorization server redirects the user-agent to the
client's redirection endpoint previously established with the
authorization server during the client registration process or when
making the authorization request.
So this means your identity server has been breached OR your registration was exploited. And you will have to worry about user being redirected to a malicious website, which could extract other important details rather than exposing authorization code.
This is emphasised in specification under Authorization Code Redirection URI Manipulation
An attacker can create an account at a legitimate client and initiate
the authorization flow. When the attacker's user-agent is sent to
the authorization server to grant access, the attacker grabs the
authorization URI provided by the legitimate client and replaces the
client's redirection URI with a URI under the control of the
attacker. The attacker then tricks the victim into following the
manipulated link to authorize access to the legitimate client.
currently i'm working on hardening the security of Vaadin project and stucked in the CSRF token, the main idea is that i have sessionID before the user login and change the SessionID after successful login to avoid session fixation, the same procedure i would like to make for the CSRF -aka XSRF- token currently i have CSRF token before the login and it remains the same after a successful login which is wrong !
now i want to reinitialize the CSRF token to new value after the successful login, my question is How to change or reinitialize the token after the successful login?
I have the following architecture.
Where:
Client - is a single page JavaScript application.
Authorisation server - is Azure AD.
Resource server - is an Azure App Service using Azure AD authentication.
All communications are secured using HTTPS.
I am using Implicit Flow to access a JWT access token from Azure AD.
https://login.microsoftonline.com/{tenant}/oauth2/v2.0/authorize?
client_id=6731de76-14a6-49ae-97bc-6eba6914391e
&response_type=id_token+token
&redirect_uri=http%3A%2F%2Flocalhost%2Fmyapp%2F
&scope=openid%20https%3A%2F%2Fgraph.microsoft.com%2Fmail.read
&response_mode=fragment
&state=12345
&nonce=678910
This JWT token is then later passed to the resource server as a Bearer authorization. The same token could be reused multiple times before it expires.
As part of the Authorize request I pass state and a nonce value.
Presently I validate the state on my client in JavaScript using a simple if:
function isValid() {
if (token.state !== expectedState) {
return false;
}
...
}
If I understand correctly the nonce is to prevent replay attacks - which I assume meant against my resource server, but perhaps also against the client.
I am unsure where (or if) I should validate the nonce.
On the server doesnt seem right, the token as a whole is being validated, and the token is meant to be reusable (within its expiry).
On the client, seems to be a better location, but is that any different to validating the state?
I am unsure where (or if) I should validate the nonce.
Of course, you should validate the nonce. Because the nonce is required and it will be returned and contained as a claim in the id_token. When you validate the id_token, you would just validate the nonce claim. Using nonce is to mitigate token replay attacks (someone who want to use token replay attack won't know the nonce, so each token has different nonce to identify the origin of the request).
There is a clear explanation for nonce for AAD v2 endpoint:
#nonce (required)
A value included in the request, generated by the app, that will be
included in the resulting id_token as a claim. The app can then verify
this value to mitigate token replay attacks. The value is typically a
randomized, unique string that can be used to identify the origin of
the request.
So, you can just validate the id_token to validate the nonce.
but is that any different to validating the state?
Yes, the effect of nonce is different from state. First, nonce will be returned in the id_token and you can validate it when you decode and validate the id_token. But state is returned in the response, not in the token. Also, state has different meaning and effect from nonce.
#state (recommended)
A value included in the request that will also be returned in the
token response. It can be a string of any content that you wish. A
randomly generated unique value is typically used for preventing
cross-site request forgery attacks. The state is also used to encode
information about the user's state in the app before the
authentication request occurred, such as the page or view they were
on.
Additional, replay attack is different from cross-site request forgery attacks. You can refer for more details about these two attacks. Then, you will understand why nonce is in the token and state is in the response.
Whether validate the nonce (token) at client
For id_token, yes, it just should be validate from the client.
For SPA with implicit flow, we can use ADAL.js to validate nonce, the id_token which contains the nonce claim to mitigate token replay attacks.
Hope this helps!
As a general point I'd recommend using the excellent oidc-client certified library to do this for you
It is tricky with Azure AD but I have a documented sample that works and that we used at my last company:
http://authguidance.com/2017/11/30/azure-active-directory-setup/
Happy to answer any questions if it helps ..
OAuth 2.0 defines "state" parameter to be sent in request by client to prevent cross-site request attacks. Same is mentioned in OpenID spec for "nonce". Apart from the fact that "nonce" is returned in ID token instead of query parameters, they appear to serve the exact same purpose. If someone can explain why they are separate
State and nonce seem to be similar. But if you dig deep, you will find that they serve different purposes.
State is there to protect the end user from cross site request forgery(CSRF) attacks. It is introduced from OAuth 2.0 protocol RFC6749. Protocol states that,
Once authorization has been obtained from the end-user, the
authorization server redirects the end-user's user-agent back to the
client with the required binding value contained in the "state"
parameter. The binding value enables the client to verify the
validity of the request by matching the binding value to the
user-agent's authenticated state
And this is used in authorization request. It enables the client to validate that the authorization response is not altered and sent by the original server which auth. request was sent. In short, it allows the client to cross check the authorization request and response.
(More elaboration : To accept authorization code response, client need to accept a response from authorization server (ex:- In web app, this can be done by a redirect and a form post to back-end). This means, our client application have an endpoint which is open and accept requests. State parameter protect this endpoint by binding original authorization requests to responses. This is CSRF protection.)
Nonce serves a different purpose. It binds the tokens with the client. It serves as a token validation parameter and is introduced from OpenID Connect specification.
nonce - String value used to associate a Client session with an ID Token, and to mitigate replay attacks. The value is passed through unmodified from the Authentication Request to the ID Token. If present in the ID Token, Clients MUST verify that the nonce Claim Value is equal to the value of the nonce parameter sent in the Authentication Request. If present in the Authentication Request, Authorization Servers MUST include a nonce Claim in the ID Token with the Claim Value being the nonce value sent in the Authentication Request. Authorization Servers SHOULD perform no other processing on nonce values used. The nonce value is a case sensitive string
As you can see, nonce value originates from the authorization request and it is generated by the client. And if nonce is included, it will be present in the token. So the client can validate the token it received against the initial authorization request, thus ensuring the validity of the token.
Also, depending on the flow type, nonce can be a mandatory parameter. The implicit flow and hybrid flow mandate nonce value. Both values are generated and validated by client application.
Why state could not be reused?
If an authorization request is captured, then the malicious party can fake the authorization response. This can be avoided by altering state parameter.
I am stating an explanation from their RFCs. The explanation is pretty straightforward.
State
An opaque value used by the client to maintain state between the request and callback. The authorization server includes this value when redirecting the user-agent back to the client. The parameter SHOULD be used for preventing
cross-site request forgery
Nonce
The nonce parameter value needs to include per-session state and be unguessable to attackers. One method to achieve this for Web Server Clients is to store a cryptographically random value as an HttpOnly session cookie and use a cryptographic hash of the value as the nonce parameter. In that case, the nonce in the returned ID Token is compared to the hash of the session cookie to detect ID Token replay by third parties. A related method applicable to JavaScript Clients is to store the cryptographically random value in HTML5 local storage and use a cryptographic hash of this value.
Reference Link: State: https://datatracker.ietf.org/doc/html/rfc6749
Nonce:https://openid.net/specs/openid-connect-core-1_0-17_orig.html
Hope this answers your question.
Nonce answers the question to the browser: Is this ID token a response to my initial request?
State answers to the backend server: did the consent really come from who I think it did?
So they answer similar questions but to different entities.
Adding to the above answers which focus on the security aspect of state and nonce, if you're implementing your own 3-legged OAuth2 workflow (client, your middleware and a Federated Identity Provider such as Facebook), your middleware might sometimes need some context. For example, when the response from the FIP reaches back to your middleware before going back to your client, you may need to know more about the details of the original request (i.e., the original request to the FIP). Because your middleware is most likely stateless, it won't be able to answer that question without any help. That's where the OAuth2 state variable comes in. You could store any string that represents the state you want to pass between all the OAuth2 jumps so that your middleware (as well as your client) can use some more context. In the case of your client, this is used for security reason. The nonce is used as part of the OIDC specification for pure security reasons.
Actually "NONCE" is enough to validate sender and response.
But before you should open the token to read "NONCE".
beacuse of this you have to accept response
if there are millions fake respose you will accept all of those to open token and read "NONCE".
But state is allready opened on response header, you can easly read state and easly reject fake response.
this is two level ceheck.
To demonstrate the difference, let's consider a situation where state exists but nonce doesn't and the attacker is able to intercept the authentication response (redirection from the Authorization Server or OIDC Provider to the client) and inject a malicious authorization code with the same state parameter. This is more likely to happen for native applications and can be mitigated by using nonce parameter approach.
OR the attacker can easily use the intercepted authorization code on the attacker's client application to log in to the victim's account. (This can also happen if nonce exists because the attacker can alter the client application to bypass nonce checking. This should be prevented by the authorization server or OIDC Provider by detecting multiple usages of the same authorization code or giving exact same consent in a short time)
PKCE can also be used as a sophisticated method, but all of the authorization servers or OIDC Providers may not support it.
As a MiiT actor, Mallory intercepts the ID token somehow and relays the token to Relying Party (aka protected service, resource server). Relying Party denies the ID token because no session cookie in Mallory's browser. The simplified relation between nonce and session, nonce = hash(session, seed_rotated_regularly)
State is a CSRF token generated by relying party in every HTTP response. As a user, Alice clicks a phishing link accidentally and her user agent is redirected to the authentication service (aka OP, IdP). Thanks to single sign-on, Alice does not notice the HTTP 302 back and forth. Assume the phishing website is allowed in redirect_uri. Relying Party can deny the HTTP request with a valid token obtain by the phishing website because state is not presented. Nonce does not work in this case because session cookie is in Alice's user agent. State cannot prevent MiiT because Mallory can get the token, state, but not the session cookie.