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CSRF is like a kafka-esque joke. Here's my take away from every CSRF article: A malicious site will load your site in an iframe, fill in your form and post it
by divtxt 14y ago
CSRF is like a kafka-esque joke.
Here's my take away from every CSRF article:
A malicious site will load your site in an iframe, fill in your form and post it. Fixing it requires some a token in your form, but I can see you don't understand how an extra hidden field in your form will make a difference so you're clearly not going to handle it correctly. You're screwed. Go home.
As far as I can tell, CSRF should have existed since javascript & frames. How have the browser vendors not fixed such a huge insecure-by-design flaw?
- phleet 14y agoThe difficulty is how to deny this happening. Pages making GET requests across domains is so common and necessary that several technology standards would have to come together to propose a real fix. Every image or script loaded from a CDN. Anyone hosting their own static assets domains. Anyone using a plugin from Google, Facebook, Twitter, Disqus uses this ability. The tech companies can't even easily create a system to whitelist sites allowed to embed them, because that would severely limit third party's ability to use their services freely and would introduce a huge performance bottleneck. I haven't seen any particularly compelling solution to solving this. Things only guarded behind a GET request can be loaded by script, link, embed, object, img and iframe tags, and all of those have legitimate reasons for loading resources cross domain without requesting permissions for each one from the user.
- divtxt 14y agoI have no problem with cross-site GET requests because I know GETs should behave as 'read-only' anyway for lots of reasons. What I don't get is how arbitrary cross-site POSTs with malicious values are allowed. As far as I can tell, anyone can post this form: <form action="http://bank.com/send_money><input http://bank.com/send_money><input name="to_account" value="SCAMMER-1234"></form> Worse, one article will tell you to only allow Referrer == "bank.com", and then another will tell you that even that is no longer enough?!!! Why can't we change the browser or the web server layer to prevent this by default?!
- eurleif 14y agoBrowsers don't prevent it because there are legitimate uses for cross-domain posts. Good frameworks do prevent it with CSRF tokens.
- divtxt 14y agoI don't want the legitimate uses prevented. The default behavior should be to prevent, and the legitimate uses should explicitly opt-in. That way, you only have to do security analysis for those explicit points.
- eurleif 14y agoBut there's existing code that would break.
- tedivm 14y agoThis to me is a server side issue- but that doesn't necessarily mean it's on the app developer. The behavior you're talking about can be set most servers directly, by adding the "X-Frame-Options" header into every request by default. Then exceptions would have to be made explicitly, by either the server admin or application developer. If anyone should change the default behavior (which I am not convinced is the case) it should be the server developers, not the browsers.
- eurleif 14y agoX-Frame-Options only prevents the page from being displayed in a frame. It doesn't prevent a page on another domain from submitting a POST request.
- tedivm 14y agoCSRF is solved very simply by using tokens for each field. If the attacking site can't load the other page, it can't pull the token out, and without the token the post gets discarded. If you've abstracted your form generation this should be super simple to add.
- ynniv 14y agoA malicious site will load your site in an iframe, fill in your form and post it. I browser cannot do this. The OP probably saw some exploit code in an ad which was served in an IFrame, but the same-domain security model will not allow you to interact with another window or IFrame that is of a different domain.