Widespread XSS Vulnerabilities in Ad Network Code | Hacker News Reader

Widespread XSS Vulnerabilities in Ad Network Code

randywestergren.com

142 pointsfinnn36 comments

We conducted a similar experiment on the top 1000 websites and found 820 unique DOM-Based XSS vulnerabilities in these sites! You can find out more about our techniques in our paper here http://www.comp.nus.edu.sg/~enricob/2015/fse15-main.pdf

So basically the top 1000 (alexa?) is completely broken and insecure?

yup pretty much. We managed to report and fix some bugs though. But it is pretty hard to get the point of contact person for some websites.

Do tools like ublock and adblock protect end users?

Douglas Crockford warned[1] us many years ago that mixing Javascript from multiple sources was fundamentally unsafe. The security model of the Javascript and the DOM was never designed for isolation within a page. If you're including Javascript from a foreign domain in the page, you're giving them access to any data in the page (and allowing stuff like this XSS problem). In most cases, this is irresponsible.

[1] https://www.youtube.com/watch?v=qfBL2sc2zUU

(re: Google Gears stuff in that talk - remember when the talk was given)

More requests to more code by more parties inherently increases attack surface area.

As a user why should I allow this for something that provides me no value (ads, tracking, js comment systems that I dont care about etc).

I can see why some people use noscript religiously and whitelist when needed

Yup. Too bad using noscript breaks the web though. An Adblocker will do for now...

NoScript doesn't break the Web. It's usually enough to allow first-party scripts, plus scripts as needed for content.

Really? I had a feeling everything is javascript heavy these days. Especially with React, angular, backbone, meteor... Maybe I should give it another try.

> Really? I had a feeling everything is javascript heavy these days. Especially with React, angular, backbone, meteor... Maybe I should give it another try.

The point is to white list scripting on websites . It allows faster browsing, lessens CPU load and memory consumption and save battery life on mobile and laptop. Most websites do not need javascript to be turned on to be browsed.

I just did it. And woosh browsing is fast, I had forgotten that part.

But then I remembered why I uninstalled it. On every site I visit I have to go through the list of scripts to allow until I can browse correctly.

You really, really need to try uBlock Origin for script blocking instead of Noscript. Enable advanced mode and default deny third party scripts.

The UI (once you understand it) is better for almost every use case, except for blocking individual scripts rather than domains.

I'm already using it, I figured noscript would be better for security though (in general, XSS can appear from anywhere, not just ads)

uBlock Origin has many more capabilities that can be found in the advanced options[0], and you can configure blocking of third party content in general that "stacks" with the default ad blocking behavior. I have uBlock Origin configured to disable all javascript by default, for example, and when I do need to enable javascript I find the uBlock interface makes it (relatively) easy to get sites working.

[0] https://github.com/gorhill/uBlock/wiki/Dynamic-filtering:-de...

I personally really enjoy using umatrix[1]. I find it allows unbreaking websites with much more ease than NoScript in my experience.

1.https://github.com/gorhill/uMatrix

Agreed. It gives you full control over the things you allow onto your browser.

I used to be a heavy NoScript user. I dumped it some time ago when they started doing a ton of weird stuff in the name of "security". Take a look at their list of features:

https://noscript.net/features

NoScript is way beyond just blocking scripts by domain at this point. They attempt to prevent things like clickjacking by subtle Javascript trickery. This broke too many web sites for me (often in infuriating and unpredictable ways) to be usable.

I use it every day without trouble

> As a user why should I allow this for something that provides me no value (ads, tracking, js comment systems that I dont care about etc).

You're presumably getting value from the page/site you're on. The person running that site is doing so because the ads, tracking, and things you don't care about allows that person to pay for the site and the time it takes to run and produce it.

What I am missing in NoScript is ability to allow 3rd party scripts (say "google.com") but just for this domain. If I allow facebook.com, I want it whitelisted only on its own domain, not elsewhere.

You should try augmenting NoScript with RequestPolicy.

Thanks, looks awesome! I'll try it out...

uMatrix has this (well, it doesn't exactly prevent script execution, but prevents fetching the scripts, which is roughly the same).

Is there anything that could fix this? Off the top of my head, browsers could encode the results of any functions that get the URL. But after encoding/decoding requests/responses and unknown server logic, the encoding may be removed.

Ad blockers would fix it. Outside of that, ad companies hiring competent devs would fix it. But I suspect they're moving too fast and breaking too many things to worry about trivial matters like XSS scripting vulnerabilities.

As a site owner, not embedding third party ads on your site would fix it. Then you only need to worry about your own code.

AdBlock and NoScript stops http://foo.bar/#1'-alert(1)-'"-alert(1)-" on every site that I've tested :)

Is there a no script plugin for chrome?

uBlock is probably enough. Yes?

If you do ad placements with iframes, that can mitigate some vectors, but then it is very hard to have full screen takeovers or many other hideous things that seem to make advertisers happy.

html5-sandbox or iframe will have you terminated from adsense, at least. don't know about the others.

> html5-sandbox or iframe will have you terminated from adsense, at least. don't know about the others.

Really? what's the justification for that policy? You'd think ad networks would want ads to be safe for users.

Probably cross-domain abuse. I'd imagine there's a few edge cases that result in behavior Google doesn't want for ads. For example, double serving, accidental clicks, ad obscuring, etc.

Their FAQ does mention that they'll grant exceptions though.

For a site owner, using properly configured Content Security Policy somewhat mitigates the risk... depends on what you can close down though, some pages have just too many functionalities.

won't affect Yahoo.com, even they show ads from that network, because it is one of the few publishers using http://www.iab.com/guidelines/safeframe/

Unfortunately - this is because the ad industry has way too many vendors (almost 0 effort required to get some shady network off the ground trafficking in bad ads) with sloppy code and bad tech.

Similar to many other industries that operate without many standards or QA/enforcement.

As if I needed another reason to block javascript and advertising.

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