[OWASP_PHPSEC] [Off topic] Recent loopholes discovered in facebook.

Abbas Naderi abiusx at owasp.org
Tue Sep 10 13:15:34 UTC 2013


Hi Shivam,
First of all, such attacks are found regularly on facebook and all other major websites. I worked in a team that reported these attacks weekly.

Second, performance is not an issue for system with security in mind. For a corp like facebook (or any other), performance is just increasing the size of their cloud infra, and its easily affordable. Security is the loss of all their reputation and data, it is not affordable.

Third. as for validation, if you google it my answer is there in StackOverflow, but the right approach is, javascript validation is only for the sake of user ease. Anything you validate in JS, you can tell your user about it without having them to wait for a request/response. Everything should be validated at server side, and you can move those validations to client-side as well.

Now some lazy ugly frameworks (Such as .NET) merge them by ajax callbacks to the server. That really hurts the performance of both the server and the application. There are frameworks that automatically convert server-side validations to javascript ones, but they can't do anything about logical checks (e.g if a username is available or taken).

Thanks
-Abbas
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On Sep 9, 2013, at 10:58 PM, Shivam Dixit <shivamd001 at gmail.com> wrote:

> Hello folks,
> 
> You all must be aware of the recent loopholes discovered in facebook. In case you are not, there were two major issues that were put forward. First, anyone can post on any other person's wall (even if you are not friend with that person) and second, you can delete any photo (even zuckerberg's) !! 
> 
> After going through the description video of both the attacks I figured out that exploits were possible just because the content received at server end was not validated. They were relying on "hidden" input fields and query strings. Attacks were performed just by manipulating these fields.
> 
> I read somewhere that sever load should be minimized by validating user's input at client side. But in application like facebook, a user makes hundreds of request to server, so is it necessary to validate all those request? For example, I am using JS Regular expressions to check if user's input is of required format or not but before inserting it in database do I need to re validate it server side because attacker might trick JS ? Will it not affect performance of application as both client side and sever side validation will take place? 
> 
> My question is, what is the correct/standard method for validation ? Client side or server side or both ?
> 
> -- 
> Cheers,
> Shivam
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