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Comment by tptacek | Hacker News Reader

Rails is no more vulnerable to XSS than any other web stack; I pay for my dev team by looking at apps all day, and they all have this problem.

You're right that taking positive action to neutralize metacharacters is a weak design. There is a setting in Rails, IIRC, that automatically h() filters outputs, but it should be the default. Just as importantly, though, even if h() is the default, you still have to audit all the places where you deliberately allow HTML output, and every app has to do that somewhere.

I'm not disagreeing with you, but I am saying that there's a major difference between mass-assignment, which is a problem Rails seems to have blundered into, and XSS, which is endemic to web apps.

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That is not true. Django and web2py both escape HTML output when variables are displayed, broadly neutralizing this attack by default.

Developers in those frameworks must explicitly say that they want to display HTML in order to have it displayed. Presumably, they have thought about this and also taken action to remove bad HTML from this output. When you have to make a choice to display it, it makes you think about this.

There is no setting in Rails to automatically escape HTML. There is Erubis, which is a replacement for Erb that can do it, and there are some XSS plugins that escape input on input or output.

I'm saying escaping HTML on output should be the default for the framework.

I don't think you read my comment carefully. The difference between XSS "susceptability" between Django and Rails is one setting (safeERB, sanitize, etc). Yes, it's a difference. I don't think it's a particularly meaningful one, because Django autoescape doesn't actually stop XSS attacks, just the stupid ones.

There's a big religious debate inside the Rails community about autoescaping, which ran aground on the point that autoescape doesn't actually stop XSS. I agree with Rails, but concede that reasonable people could think otherwise.

It's hard to see how reasonable, well-informed people could think that mass-assignment was a good default feature.

Can you give an example of an XSS attack that isn't prevented by auto-escaping (other than the UTF-7 one)?

All the attacks that occur in the outputs that you can't auto-escape, because they need to contain HTML by design.

It's not the "escape" that's the problem, it's the "auto".

Gotcha, the HTML sanitization problem. Django doesn't even attempt to solve that, which is probably a bad idea since it inevitably means people will use the various insecure libraries that are out there on the 'net. The trouble is it's /really hard/ to do right - I'd be uncomfortable shipping a sanitizer with Django because I'd worry that some weird undocumented IE parsing error would allow nasty code to slip through and result in a 0-day exploit against the entire framework.

People tend to oversimplify this down to "how to accept HTML in user input", but the problem is more general: lots of applications have two-stage rendering sequences, where data is accepted and stored as HTML, and rendered later.

In the case of web2py there is an object called XML, text passed to the view inside XML is not escaped otherwise it is. You can also do XML(text,sanitize=True) and you can specify which tags and with tag attributes should be allowed. The sanitizer that ships with web2py is the one developed by Josh Goldfoot and posted on activestate, recipe 496942.

OK, I agree with you that escaping by default only stops some attacks, and if the developer's response is to simply disable the escaping every time they need to display HTML it's not going to be much help.

However, I would argue that nearly every Rails app does have susceptibility to these "trivial" attacks because Rails does not force you to think about when you want to display HTML.

I also agree that people disagree on this. But I still feel the default should always be the secure one.

I don't think that's a crazy point of view. I'm ambivalent. You have easier, better ways to win security arguments about Rails than the lack of one relatively trivial default setting, though.

I would actually say Django has a very poor HTML escaping facility. (Though, better than Rails, for what that's worth.)

I feel like I've used template languages that actually understand XML (or HTML) and thus have context sensitive escapes. It was probably written in something gross like Java, so URLs were output verbatim in links, while say instances of "/search?q=" + someVariable would url escape someVariable in links, and html escaped in tag contents.

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