Comment by unamashana | Hacker News Reader

Comment by unamashana | Hacker News Reader

Hey HN!

We made a chrome extension to notify you of new comments on your stories and comments.

Once installed, it adds a bell to HN's header and shows new notifications in real-time. Clicking on the bell loads a notification inbox with easy access to all your notifications with a clear distinction between the read/unread ones.

Unlike some other options like HN replies, here are the key differences

We don't ask for your email address - we use the HN cookie to identify you. There is no setup beyond adding the extension. Apart from on-page notifications, you can also subscribe to web-push notifications.

We are using HN Firebase API to get a real-time feed of notifications, and our startup, [MagicBell (YC W21)](https://magicbell.io), to power the notification inbox. We built this extension because we found it hard to keep track of our [Launch HN thread](https://news.ycombinator.com/item?id=26037645) comments.

We want to build a version for Firefox & Safari, and if you'd like to know when they go live, please follow us on [Twitter](https://twitter.com/magicbell_io). Dozens of early users have tested the extension, but if you run into any issues, please tweet at us, and we'd be more than happy to help you with it. We'd also love to hear your ideas on additional functionality you'd like to see.

>We don't ask for your email address - we use the HN cookie to identify you

does this extension contact any servers apart from hn itself?

It contacts magicbell.io. HN does not provide an API that we can query in real-time to fetch your notifications.

I just checked the cookies on hn and there's only one, with the format of:

    user=gruez&[redacted]

Are you sending the entire session cookie, or just the part with the username?

The entire session cookie to validate your login. Unfortunately there is no other reliable way to do.

That sounds dangerous. By sending the full cookie you're allowing yourself to hijack any of your user's sessions. That's a big security risk. Is there a reason why you need to "validate" someone's login? If someone wants to get notified about my comments, so what? There's nothing secret about it, they can just go to https://news.ycombinator.com/threads?id=gruez and get a live feed.

While the comments themselves are open, their state in your MagicBell inbox isn’t. If we didn’t have a way to validate identity, we won’t be able to make sure your notifications can’t be deleted/marked read by someone else.

Why not drop a local cookie yourself for state?

That doesn’t prevent someone from being able to impersonate you. The only alternative would be for HN to provide oauth access to your profile info.

Perhaps you could hash the session id, with a secret salt on server side. Then you could discard the original and store and pass along the hashed session id. That way, anyone you send it to would not be able to impersonate the hn user. You could also hash with a different salt before sending to a 3rd party so that they would not be able to impersonate someone's account in your extension.

Just to be clear, we simply validate your session by requesting the page with your cookie and seeing if we get a logged in page. We never send your info to any third party.

You can claim whatever you want to claim, we unfortunately have no way to ensure that this is true.

This is a security hazard, period.

While the feature is nice, and I like the design of the notification dropdown, this is a risk I (and probably many) won't take.

For the purposes of authenticated interactions between HN and the user, you are the third party who now has full access to the user's account. App/extension stores generally take a dim view of/outright prohibit this because of its high abuse potential.

I see. That makes more sense. I understood from another post that you were also passing it along to another service.

Aren't you (magicbell) gaining the persistent ability to impersonate any HN user who installs this extension? That seems like a much more serious problem than someone being able to impersonate your magicbell hn notifications. It sounds like you're saying that because HN has no fine-grained oauth delegation, it's ok to silently hijack users' HN accounts. That can't be right.

> That doesn’t prevent someone from being able to impersonate you.

But why is that a problem? If somebody wants to get notified of replies to my comments, let them.

I understand why you need a unique token so that collisions don't happen, but that token doesn't need to be one-to-one unique with Hackernews usernames. It's OK to have two unique tokens that are separate from my session cookie that point to me as a user, and to have the "read" status be per-token, not per-user.

More to the point, why does this read status and everything need to be stored serverside for a browser extension? Where are you putting this information where you're worried about collisions with random internet users, why have it leave the browser at all?

You don't need a unique token if you're not storing everything in a centralized location off-device, the browser profile that's using the extension is itself the unique token. Why does anything need to be transmitted anywhere? Let the extension store the read statuses locally on my device, then there's zero chance of them colliding with anybody else's installation. Even if someone turns on push notifications, the push API already sends you a unique, randomized device ID/key. What's the reason why you can't push an RSS-style feed out to the device using that ID?

I completely agree with all of this. It can be done without any of this server-side stuff.

But to answer the question:

> Why does anything need to be transmitted anywhere?

It's because the extension is written by, and "powered by", MagicBell. They are writing it to bring attention to their product concept, where notifications like this are all handled by them.

That's totally fair, but it raises a followup question because from what I can see, MagicBell has user accounts.

So that's also a unique identifier that they could use to prevent collisions. They could have a randomized ID generated locally for this "promotional" extension, and if a user creates an account on MagicBell at that point they could migrate them over to an official user ID.

If this is being tied to a real backend service, I'm almost more confused why it's important to transmit my session cookies around.

That's a complete deal breaker.

Also, your chrome web store page says "The publisher has disclosed that it will not collect or use your data". But you do collect and use users session cookie.

And your linked privacy page has no content (it is literally an empty page at the current time): https://magicbell.io/privacy-policy.

Sorry about the oversight in the chrome store page. We'll fix that asap. The privacy policy page has a link to the privacy policy hosted by Iubenda if you have Javascript disabled. If you have Javascript enabled, the privacy policy renders inline.

I do not disable javascript but use an adblocker.

Really? Because I thought of one in the time it took to read this comment. Your extension has access to the page contents, which you can use to determine the username. It’s right in the nav. You can validate that it’s authenticated by a quick look at the profile link to see that it’s editable. Cache that boolean with a hash of the cookie for subsequent validation and you’re all done, without sending anything to your own server.

Why do you need a cookie at all? All the HN comments are public so once you’ve ascertained the handle you can query the API for any user to diff for changes.

Reply on news.ycombinator.com