Comment by atom_enger | Hacker News Reader

Comment by atom_enger | Hacker News Reader

I remember reading this when I was the sole Infrastructure Engineer for Reverb.com. I knew we were being attacked and I knew we had issues but I didn't have any idea where to start. This article sparked my interested in Cyber Security and helped me find a bug in the website that allowed me to set the CEO's credit card as a primary card on my account in production. That was an amazing day.

All I had to do was modify a post parameter in flight and the backend would accept it. Turns out this is what is known as an "unscoped find". More info here: https://brakemanscanner.org/docs/warning_types/unscoped_find...

Thanks to the author of the article for inspiring me to dig in the rails codebase and find vulnerable patterns that I could exploit. Thankfully I was able to pivot into a cyber security focused career and I credit this article for starting me down that path.

Rails has a few things going for it that other languages and frameworks don't but it still lets you shoot yourself in the foot if you're not careful. I ended up writing a blog article about preventing XSS in rails as a direct inspiration from the OPs article: https://product.reverb.com/stay-safe-while-using-html-safe-i...

Just because this article is old doesn't mean it's not useful. Thanks for posting!

The unscoped find issue is fairly easily solved by using devise's current_user in combination with something like cancancan. Let them send anything as a param but have the controller blow up if the user doesn't have permission to access it.

I suspect an insane number of websites are validated only by the frontend and can be exploited like this.

Can't this be solved with scoping via the pundit gem, as well?

You'd suspect right :) I've had a huge number of bounties from this as a result of finding the pattern first on Reverb.

It should be said that an "unscoped find" is a generic and serious design flaw, which isn't specific to Rails.

It's on the current OWASP top ten as one case of "Broken Access Control" (scenario 1): https://owasp.org/www-project-top-ten/OWASP_Top_Ten_2017/Top...

(In at least one prior edition, it had an entry of its own as "Insecure Direct Object Reference".)

At some point before that, it was known as "forced browsing", though that name took on a more particular meaning and then fell away. It is by far the most common software vulnerability.

In practice, XSS is largely mooted by the rise of front-end frameworks like React, Vue, and Angular, which are the modern norm for delivering UI (I don't think we have a single client that uses serverside-templated-HTML anymore), and the front-end framework approach is better than the Rails/Django approach; I'm very unlikely to find XSS in a simple React app, but not at all unlikely to find it in a Rails app, because people always dip out of the XSS protection to do programmatic tags.

I think making the mistake of "unscoped find" that "atom_enger" was referring to is just as easy a mistake to make when writing a REST backend (to support a SPA front-end framework) as when using a traditional non-SPA web framework.

It's tempting, when writing a REST backend, to respond to e.g. "PUT /message/:id" by just executing "UPDATE ... WHERE message_id=?" from the parameter, without checking that that message belonged to the user whose credentials have been used to access the call.

That's possible with a non-SPA web framework, and it's also possible when writing REST backends.

Authz bugs are the most common bugs in every application, and no framework has a particular edge on stamping them out. I'm just responding to the claim about Rails having a security edge due to XSS protection, which it does not; in fact, it's become somewhat the opposite.

> I'm very unlikely to find XSS in a simple React app

I do offensive security. A lot of developers are ignorant of when/how React apps tend to be XSS vulnerable. Since it has a reputation as being 'safe' from XSS, devs often assume it's just something they don't have to worry about.

This has led to a small renaissance of XSS bug bounties on sites like hackerone, where you see a lot of specialists who just go around finding obvious, common XSS vulns in eg Angular apps.

I do offensive security. My direct experience, in my audit workload of web applications, which I've had pretty steadily (with some short gaps) since 2005, is that XSS vulnerabilities are far rarer in React applications (regardless of backend) than they are in Rails apps. It's not hard to see why: Rails begs you to disable XSS protection to get anything interesting done in HTML (basically, any time you dip out of Erb or Haml), there aren't a similar number of use cases for overriding React's control of the DOM (because the whole point of React is to give you safe control of the DOM), and when you do, in React, you do it (almost all of the time) with "dangerouslySetInnerHtml" (though this holds just as true with Vue and "v-html".

It's not my argument that there's no XSS in React apps. I've definitely found React XSS. But I assume any Rails app I test will have it somewhere, and, based on experience, I do not have that assumption about React applications.

I completely agree with your overall point, I was just making an aside about the tendency of more inherently secure systems to sometimes lead to dev laziness. The same thing can happen to Rust devs, but I wouldn't argue that it isn't way more secure generally than C.

Thanks for sharing this. I'm new-ish to web dev and have considered a similar pivot. Also a customer on Reverb so that's cool to hear your story and read that write up you linked.

Don't get me wrong: I'm really glad that you caught the bug in your code before anyone lost an eye.

However, a critical summary of your situation could be "improperly used an advanced method that exists for the specific purpose of marking a string as having been certified safe, potentially allowing an XSS that would have otherwise been successfully filtered out by Rails' extensive anti-XSS mechanisms".

I was super upset when one of the drives in my RAID 0 set went, but it was still my bad for not learning that RAID 0 isn't mirroring. (Hint: the 0 is the amount of information you can recover in case of failure.)

My point is just that you can't really claim that Rails dropped the ball here. If there are footguns installed, it's because you installed them (and didn't read the manual for html_safe).

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