On Jul 2, 2014, at 7:29, Torsten Irländer <tor...@irlaender.de> wrote:
> I need to protect some of my GET requests in the application against CSRF attacks.
> AFAIKS many (if not all) resources writing about CSRF protection say that this is usually only need to be done for POST requests which will change data or the state of the application. However I feel the need to protect some GET requests because they return sensitive information which must be prevented because of e.g data privacy. I think i need to provide the token within the GET parameters of the request. I am using per request CSRF-Tokens, so the issue of disclosure the tokens in the URL as described on OWASP [0] should be not a big deal.
The reason you use CSRF tokens is to protect a web form from being submitted from a 3rd party site, and thus invalid data being inserted into your site, since JavaScript can make POST requests, this is generally a good idea to stop a web spammer from spamming your site with invalid data or spam.
GET requests are (SHOULD be) idempotent and don’t allow an attacker to insert data into your site, nor modify data.
Even if you were to use CSRF tokens, it wouldn’t add any extra protection to your site. You should be checking permission for the current logged in user, setting appropriate cache values and everything along those lines before you return the page to the user, if the user doesn’t have access because of permissions, don’t display the data.
>
> Now I am thinking about the best way to do this in pyramid.
>
> Currently i am thinking about implementing the following simple idea:
>
> 1. Write a wrapper method for the various "route" methods in pyramid.request which adds the current csrf token to the GET parameters.
> 2. Check the token by providing the check_csrf parameter to the add_view methood.
>
> Do you think this is a good approach, or what would be your advice?
I don’t think adding CSRF tokens to a GET request makes sense from a security stand-point.
Am Mittwoch, 2. Juli 2014 17:00:02 UTC+2 schrieb Bert JW Regeer:
On Jul 2, 2014, at 7:29, Torsten Irländer <tor...@irlaender.de> wrote:
> I need to protect some of my GET requests in the application against CSRF attacks.
> AFAIKS many (if not all) resources writing about CSRF protection say that this is usually only need to be done for POST requests which will change data or the state of the application. However I feel the need to protect some GET requests because they return sensitive information which must be prevented because of e.g data privacy. I think i need to provide the token within the GET parameters of the request. I am using per request CSRF-Tokens, so the issue of disclosure the tokens in the URL as described on OWASP [0] should be not a big deal.
The reason you use CSRF tokens is to protect a web form from being submitted from a 3rd party site, and thus invalid data being inserted into your site, since JavaScript can make POST requests, this is generally a good idea to stop a web spammer from spamming your site with invalid data or spam.
I think this is totally clear to me.
GET requests are (SHOULD be) idempotent and don’t allow an attacker to insert data into your site, nor modify data.
Well but inserting or modifying data is only one option for an attacker. In many cases retrieving data is much more valuable for an attacker. This is the reason why I thought I should also prevent CSRF-Attacks on GET requests...
Even if you were to use CSRF tokens, it wouldn’t add any extra protection to your site. You should be checking permission for the current logged in user, setting appropriate cache values and everything along those lines before you return the page to the user, if the user doesn’t have access because of permissions, don’t display the data.
I suppose you are right, but I don't get it... Maybe someone could explain it to me.
Imagine the following scenario:
Alice has access to web application with super secret data. The application is secure, permissions are checked properly etc. Alice is allowed to read the secret data.
Now Bob sends Alice a malicious Email with some XSS Code included. This code calls a URL which retrieves the super secret data in the application and sends this data back to Bob.
Alice usually reads her Mail in a webmailer in the same browser where she already has logged in in the application. She opens Bobs Mail and triggers the execution of the malicious code.
Isn't this a realistic CSRF attack?
>
> Now I am thinking about the best way to do this in pyramid.
>
> Currently i am thinking about implementing the following simple idea:
>
> 1. Write a wrapper method for the various "route" methods in pyramid.request which adds the current csrf token to the GET parameters.
> 2. Check the token by providing the check_csrf parameter to the add_view methood.
>
> Do you think this is a good approach, or what would be your advice?
I don’t think adding CSRF tokens to a GET request makes sense from a security stand-point.
If the scenario above is realistic, I see the absolute need for adding them.
But again: As almost everyone is only talking about POST requests in connection with CSRF I think its me who is missing some important point here.
But a really like to understand this. So please bring some light in here
Torsten
--
You received this message because you are subscribed to the Google Groups "pylons-discuss" group.
To unsubscribe from this group and stop receiving emails from it, send an email to pylons-discus...@googlegroups.com.
To post to this group, send email to pylons-...@googlegroups.com.
Visit this group at http://groups.google.com/group/pylons-discuss.
For more options, visit https://groups.google.com/d/optout.
Am Mittwoch, 2. Juli 2014 17:00:02 UTC+2 schrieb Bert JW Regeer:
On Jul 2, 2014, at 7:29, Torsten Irländer <tor...@irlaender.de> wrote:
> I need to protect some of my GET requests in the application against CSRF attacks.
> AFAIKS many (if not all) resources writing about CSRF protection say that this is usually only need to be done for POST requests which will change data or the state of the application. However I feel the need to protect some GET requests because they return sensitive information which must be prevented because of e.g data privacy. I think i need to provide the token within the GET parameters of the request. I am using per request CSRF-Tokens, so the issue of disclosure the tokens in the URL as described on OWASP [0] should be not a big deal.
The reason you use CSRF tokens is to protect a web form from being submitted from a 3rd party site, and thus invalid data being inserted into your site, since JavaScript can make POST requests, this is generally a good idea to stop a web spammer from spamming your site with invalid data or spam.
I think this is totally clear to me.
GET requests are (SHOULD be) idempotent and don’t allow an attacker to insert data into your site, nor modify data.
Well but inserting or modifying data is only one option for an attacker. In many cases retrieving data is much more valuable for an attacker. This is the reason why I thought I should also prevent CSRF-Attacks on GET requests...
Even if you were to use CSRF tokens, it wouldn’t add any extra protection to your site. You should be checking permission for the current logged in user, setting appropriate cache values and everything along those lines before you return the page to the user, if the user doesn’t have access because of permissions, don’t display the data.
I suppose you are right, but I don't get it... Maybe someone could explain it to me.
Imagine the following scenario:
Alice has access to web application with super secret data. The application is secure, permissions are checked properly etc. Alice is allowed to read the secret data.
Now Bob sends Alice a malicious Email with some XSS Code included. This code calls a URL which retrieves the super secret data in the application and sends this data back to Bob.
Alice usually reads her Mail in a webmailer in the same browser where she already has logged in in the application. She opens Bobs Mail and triggers the execution of the malicious code.
Isn't this a realistic CSRF attack?
Am 02.07.2014 23:01, schrieb Torsten Irländer:
Am Mittwoch, 2. Juli 2014 17:00:02 UTC+2 schrieb Bert JW Regeer:
On Jul 2, 2014, at 7:29, Torsten Irländer <tor...@irlaender.de> wrote:
I guess that most people only talk about protecting post request since they _think_ that the web application would be programmed this way, that all actions (like deleting all contacts) would only be accessable via a POST request. So they THINK there is no need in protecting GET requests. But I know web applications that also change data via GET requests.
Buttriggering a GET request that only _reads_ your addresses, would display the addresses and not change them. (Well, Maybe some code can also steal the addresses)
Nevertheless I absolutely recommend to also protect GET requests against CSRF!
On Wed, Jul 2, 2014 at 2:01 PM, Torsten Irländer <tor...@irlaender.de> wrote:
Am Mittwoch, 2. Juli 2014 17:00:02 UTC+2 schrieb Bert JW Regeer:
On Jul 2, 2014, at 7:29, Torsten Irländer <tor...@irlaender.de> wrote:
> I need to protect some of my GET requests in the application against CSRF attacks.
> AFAIKS many (if not all) resources writing about CSRF protection say that this is usually only need to be done for POST requests which will change data or the state of the application. However I feel the need to protect some GET requests because they return sensitive information which must be prevented because of e.g data privacy. I think i need to provide the token within the GET parameters of the request. I am using per request CSRF-Tokens, so the issue of disclosure the tokens in the URL as described on OWASP [0] should be not a big deal.
The reason you use CSRF tokens is to protect a web form from being submitted from a 3rd party site, and thus invalid data being inserted into your site, since JavaScript can make POST requests, this is generally a good idea to stop a web spammer from spamming your site with invalid data or spam.
I think this is totally clear to me.
GET requests are (SHOULD be) idempotent and don’t allow an attacker to insert data into your site, nor modify data.
Well but inserting or modifying data is only one option for an attacker. In many cases retrieving data is much more valuable for an attacker. This is the reason why I thought I should also prevent CSRF-Attacks on GET requests...
Even if you were to use CSRF tokens, it wouldn’t add any extra protection to your site. You should be checking permission for the current logged in user, setting appropriate cache values and everything along those lines before you return the page to the user, if the user doesn’t have access because of permissions, don’t display the data.
I suppose you are right, but I don't get it... Maybe someone could explain it to me.
Imagine the following scenario:
Alice has access to web application with super secret data. The application is secure, permissions are checked properly etc. Alice is allowed to read the secret data.
Now Bob sends Alice a malicious Email with some XSS Code included. This code calls a URL which retrieves the super secret data in the application and sends this data back to Bob.
Alice usually reads her Mail in a webmailer in the same browser where she already has logged in in the application. She opens Bobs Mail and triggers the execution of the malicious code.
Isn't this a realistic CSRF attack?I don't think it's a common one.The webmail would have to execute scripts inside the email. That seems problematic to start.
Even if it did, any request to the application would be cross domain unless the webmail is on the same domain.
That means that, unless you explicitly set CORS headers, that request won't include cookies. So, there's no session available through which to receive private data.
Am 03.07.2014 08:43, schrieb Torsten Irländer:
Am Donnerstag, 3. Juli 2014 00:32:15 UTC+2 schrieb cornelius:Am 02.07.2014 23:01, schrieb Torsten Irländer:
Am Mittwoch, 2. Juli 2014 17:00:02 UTC+2 schrieb Bert JW Regeer:
On Jul 2, 2014, at 7:29, Torsten Irländer <tor...@irlaender.de> wrote:
I guess that most people only talk about protecting post request since they _think_ that the web application would be programmed this way, that all actions (like deleting all contacts) would only be accessable via a POST request. So they THINK there is no need in protecting GET requests. But I know web applications that also change data via GET requests.
Buttriggering a GET request that only _reads_ your addresses, would display the addresses and not change them. (Well, Maybe some code can also steal the addresses)
That's the point. If those addresses are not public and considered to be only visible to authenticated users, than such a GET request is a large security issue ( if such a request is realistic at all )
Nevertheless I absolutely recommend to also protect GET requests against CSRF!
Ok, and how would you do it in pyramid?
Torsten
Hi Torsten,
i am not sure, if I would rely my web application security completely on the client/browser side.
I think your example with the email was a bit to complicated.
The much simpler and thus better example is directly at wikipedia:
https://en.wikipedia.org/wiki/Cross-site_request_forgery#Example_and_characteristics
And it is not necessarily important to read any action but to trigger an event.
Imagine your companies web application to configure the firewall.
You could easily "guess" the URL to disable the You**** blocking and make your administrator click this URL.
If you are lucky and the administrator is logged in in the bad firewall UI and he clicks the image/link - bingo.
OWASP recommends using a token in addition to the cookie, that is verified on the server side.
Thus you (the attacker) are not able to construct the link with the token, which you can not guess.
I did it in pylons once using repoze.who, which issued an authenticating token.
@Bert: admitted, maybe there were many unlucky side effect, but CSRF was possible in this case.
As I did not wanted to keep track on synchronizer tokens on the server side, the original web application read the session cookie from the browser and added the this token as parameter for the further requests. Thus the server only needs to compare the cookie and the parameter.
Admitted again: At this point I rely on that a rogue website is not able to access the cookies from my web application. But I assume this to be robust.
As I did not wanted to keep track on synchronizer tokens on the server side, the original web application read the session cookie from the browser and added the this token as parameter for the further requests. Thus the server only needs to compare the cookie and the parameter.
Ok, and how did you add this token as parameter the further requests? Did you enhance the url generation in Pyramid?
If your GET requests are not idempotent (i.e. They will always return the exact same response, and don’t modify any state) there is no cross site request forgery that can happen.
I think the general conclusion that GET request are not vulnerable is only true under certain circumstances. And I as a implementer do not want to think about every GET request if it might get a threat in some situations or future scenarios. So I would welcome a solution in a webframework which offers me the option to add such CSRF protection in GET requests if I want it - regardless if it is really needed for the request.
On Tue, Jul 8, 2014 at 2:27 AM, Torsten Irländer <tor...@irlaender.de> wrote:
I think the general conclusion that GET request are not vulnerable is only true under certain circumstances. And I as a implementer do not want to think about every GET request if it might get a threat in some situations or future scenarios. So I would welcome a solution in a webframework which offers me the option to add such CSRF protection in GET requests if I want it - regardless if it is really needed for the request.
There's no way to do that without breaking HTTP, basically. Since there is no POST data, the only place you could add a CSRF token is in the URI itself. Obviously, no one would be able to save a bookmark to such a page, or just navigate to it by knowing the URI.
Once you're adding random-ish data to the URI for this purpose, you've broken it's design as a resource identifier--it's not a universal identifier, it's a secret token.
If a GET request is modifying state in any meaningful way that needs protection, then it shouldn't be a GET request.
Not there's any technical hurdle to doing what you want, but you're fighting the basic concepts underlying HTTP at that point. If you can get on board with using HTTP verbs for what they are designed for, there is a lot beautiful simplification that falls out. Be a Zen programmer and go with the flow. Make your GET requests idempotent and safe. Protect your POST form submissions using a CSRF token. Relax in the evening knowing you're probably not going to get attacked tonight, because you used good design