Begin by reading up on Rails.

Mass assignment is a fairly normal thing to do, any parameters you want the model to ignore can be marked as so in the model and then mass assignment will work anywhere. Rails loves DRY.

Since the only way in which one can get wrong arguments is if somebody is hacking you (or attempting to do so) in which case just throwing an error at them is a fair thing to do.

Blanket accepting POST data to insert into your database is a terrible idea.

Rails gives you attr_accessible and attr_protected to alleviate this problem. Protip: the one from those two that you suggested to use is just as terrible an idea as allowing blind POST into your database. Blacklisting is always the wrong approach to security. I don't care if you have to repeat yourself and type more characters: use the whitelisting of attr_accessible.

But even if they're using attr_accessible to whitelist parameters, the failure mode here would have been exactly the same.

The real culprit is Apple. It's just not ok to add unexpected parameters to people's POSTs. If anything, they should have put it in an HTTP header instead.

I'm a Python/Django guy so I'm not intimately familiar, but is that really the case? I was under the assumption that the handler wouldn't pass any POST vars not in attr_accessible to the model. In which case additional, unexpected ones would become silently dropped.

According to http://guides.rubyonrails.org/security.html#countermeasures you're entirely correct that it won't raise any error, although the keys won't be dropped: attr_accessible drops the attributes when mass-assigned to a model, they're still available in the params hash.

> Mass assignment is a fairly normal thing to do

No, it's an abnormal thing to do and a security hole.

> any parameters you want the model to ignore can be marked as so

Which is complete insanity.

> Rails loves DRY.

Yes so does PHP, hence register_globals.

That's on the "idiotic" side of "I don't want to write stuff", and even the Rails staff stopped defending this insanity back in March.

If you want to argue against facts, please go elsewhere. Mass assignment is widely used in Rails.

Just because something is widely used does not mean it is not a security hole. Mass assignment is a security hole, plain and simple- in Rails and anywhere else.

> Mass assignment is widely used in Rails.

And register_globals was widely used in PHP, that does not make it anything but moronic.

I don't think register_globals has been widely used for at least 10 or 12 years. It's been deprecated for a while and was removed completely in 5.4.0.

Hence "was". It was widely used at one point, if only because it was enabled by default until 2002 (disabled by default was introduced in PHP 4.2)

I'm not a Rails guy, so you'll have to forgive ignorance here. Are you telling me that Rails only lets you blacklist parameters, not whitelist?

Because that seems entirely the wrong way around.

EDIT: looked at the link posted elsewhere here[1] and ound that it is possible to whitelist using "attr_accessible". Please tell me people know about and use this.

[1] http://guides.rubyonrails.org/security.html#mass-assignment

You can do either. The default used to be blacklist, but that was changed to whitelist recently.

You can do either. Whitelist is obviously preferred.

It allows either.

Sure, throw an error, but not a 5xx error. ISE 500 indicates that something went wrong on the server, not on the client. 400 Bad Request maybe?

I, for one, don't like having my application error logs polluted by script kiddies running against my wall...

Isn't this default Rails behavior? (despite sounding like something people would make fun of PHP for doing)

It used to be, and was recently changed after they realized that even PHP had disabled `register_globals` years ago (also, after they realized even Github, one of the biggest Rails site out there, had left this hole wide open and a guy used it to demonstrate the issues on the rails repo/account, which was very funny drama: https://github.com/rails/rails/issues/5239 http://erratasec.blogspot.be/2012/03/rubygithub-hack-transla...)

This (mass-assignment) is fairly standard Rails-fu, so its fair to assume that this could affect a lot of apps out there.

Correct me if I'm wrong, but isn't it pretty much always a bad idea to do it blindly, and the defaults are considered a security problem by the Rails project itself?

http://guides.rubyonrails.org/security.html#mass-assignment

Hey now, don't go bringing facts into this thread -- I've already been downvoted hard for, apparently, not knowing what I'm talking about when saying that this is a security issue. So obviously the Rails team don't know what they're talking about either.

He just linked to an article that explains how to do it safely.

update to reply because of downvotes:

1) butterfly knives are very useful tools

2) mass assignment can be used safely out of the box in rails post v3.2.3. To use it, you have to explicitly add parameters to the whitelist or disable the whitelist. The article is there to explain why disabling the whitelist is a bad idea.

Sure, just like butterfly knives are safe because you can find some safety tips online.

Edit to reply to edits: Mass assignment is still dangerous "out of the box" since you have to switch on the whitelist behavior by calling attr_accessible on your model classes. In the security guide, the older, more dangerous, attr_protected is introduced first.

I think every rails dev should be familiar with the security guide, but more than that I wish that security was the default. While anybody is free to make an app as insecure as they wish, it should be the exception rather than the default.

You're talking about the old behaviour. New rails apps have config.active_record.whitelist_attributes set. That means that models without attr_acessible statements will throw an error if mass-assignment is attempted. IOW, they've done exactly what you asked for. They should have done it years ago, but they did the right thing after it blew up in their face.

You say "standard Rails-fu", I say security hole. Let's call the whole thing off?

No because you don't know what you are talking about.

I see. So that whole big mass-assignment security issue that exposed GitHub a while back -- that just didn't happen? Writing code in this style is perfectly safe?

Writing code in this style is perfectly safe if you do it correctly. GitHub didn't, so the defaults were changed to make it harder to do it incorrectly.

UPDATE: editing to reply since hn won't let me reply directly because the thread is to deep, yet I'm getting downvotes

It's not a tautology. Some things are safe even if you do them wrong. Some things are unsafe no matter how you do them.

Rails changed the defaults so that now you have to deliberately decide to do things unsafely. Rails before 3.2.3 fails un-safe in this scenario, but later versions fail safe. Rails 4 uses a different solution that's even harder to screw up.

"Writing code in this style is perfectly safe if you do it correctly."

That's a tautology.

In general you can't count on code being written "correctly", so this isn't a defense. It is better to have systems that degrade gracefully in the face of humans and their idiosyncrasies, rather than those that fail-unsafe, because you can't build your security system on the assumption that your code will be written by superhumans.

Should all database use be frowned upon because injections are possible if you don't use them correctly?

I hope you realize that this is the identical argument PHP developers made whenever someone brought up how insecure the base language, libraries, and configuration were.

Users of a framework should have to go out of their way to make themselves insecure. It shouldn't be insecure by default.

This isn't a Rails issue, it can affect any web framework. And it's a security flaw every single time mass assignment is used without whitelisting.

> This isn't a Rails issue, it can affect any web framework.

Not exactly. Most web frameworks don't have a built-in "mass assignment", let alone enable it by default.

Well, true. I wonder how many people pass their models straight into a schema-less database without any checks?

like you are holding iphone4 wrong? If it's an app doing RESTful API calls via HTTP POST then it should have 100% control on HTTP parameters.

Watch next time Apple alter some http headers and break your API.

Although I agree with you that Apple should not alter HTTP POST parameters in-flight, the server side application must expect the client to be untrusted. Anything can connect to the server socket, not just its RESTful app on iOS.

What does this have to do with client trust? They're expecting the client to access their API a certain way, and the client is sending what is arguably a malformed request. This is, surprise, causing an error to occur.

Hard to tell from the post, but it sounds like Rails gave an Exception because it couldn't find should_group_accessibility_children, but that suggests that it would act on something it could find.

If there was a parameter that gave a user admin access, then Rails might accept such a parameter and that might be used to take control of the app.

It's similar to what happened to Github.

https://github.com/rails/rails/issues/5228

I would think that the API would validate the POST parameters, ignore unexpected parameters and give errors for malformed expected ones. Taking it a bit further the developer should then be notified of malformed POST parameters being present and decide if it is a bug or an attack.

You never ever ever ever blindly trust the client to behave a certain way.

They are not. They give an error. The only issue is that a middle man is fucking with them.

Except they "give an error" because the provided field doesn't exist in the database. Ignore for a second that half the reposts would break websites if an unexpected parameter yield an error instead of being ignored, if an untrusted client sent an "id" field, that would go through like hot steel through melted butter.

Actually Rails have a feature to mark certain parameters as not mass assignable.

Which is also broken.

Well. The likeliest thing is that there is no "middle man fucking with them". The likeliest thing, since it's an iOS app posting to their API, is that they're introspecting a client-side object to get the values they care about. And that they're blacklisting values they know they don't want, rather than whitelisting values they know they do want.

Which meant that when a new property showed up their app blindly submitted it to their web API, and their web API blindly accepted it because it was doing mass assignment, and that's when the API broke.

Which really just hammers home the point people have been trying to get you to see, which is that these types of idioms -- mass assignment, blind trust of client-supplied data, blacklisting instead of whitelisting -- are really serious problems that should not be encouraged, and should not be swept under the rug.

Apple isn't injecting this into the request. It's an object property and the application developers are doing something in their app that is iterating over and Objective-C object and creating a POST request from it. I guarantee it.

Form fields by way of application/x-www-form-urlencoded generally shouldn't be trusted wholesale. In the Wild, Wild Internet, you'll see things like 3rd party JavaScript add hidden fields, etc.

Instead of modifying at the middleware or persistence layers, copy relevant fields out of the POST hash into an intermediate hash. Which, generally, will be more secure anyways.

If your API breaks because an extra unrecognized parameter is included, Apple didn't break your API, you did.

Can you elaborate on why you think invalid API parameters should be silently ignored? I can see arguments for both sides, but none of them would make the API "broken" in my mind.

"The programmer should always have complete control", if the API is broke, the programmer has lost control.

From a security and usability perspective, the programmer must always be in ultimate control of what code is being executed. If it's "parameters", an API should be explicitly requesting any or all parameters, and completely ignoring unknowns. If the API is scanning for unknown parameters or even worse scanning for parameters to invoke variable named function calls (it happens a lot), at best; your API is wide open for attack. (This was a major attack vector in some Wordpress APIs in the recent past.) In the meantime, the unknown parameter just causes the program to break, and why would any programmer allow that if it's so easily preventable.