Categories: featured addons

Developer Spotlight: Port Authority

Port Authority gives you intuitive control over global block settings, notifications, and allow-list customization.

A few years ago a developer known as ACK-J stumbled onto a tech article that revealed eBay was secretly port scanning their customers (i.e. scanning their users’ internet-facing devices to learn what apps and services are listening on the network). The article further claimed there was nothing anyone could do to prevent this privacy compromise. ACK-J took that as a challenge. “After going down many rabbit holes,” he says, “I found that this script, which was port scanning everyone, is in my opinion, malware.”

We spoke with ACK-J to better understand the obscure privacy risks of port scanning and how his extension Port Authority offers unique protections.

Why does port scanning present a privacy risk?

ACK-J: There is a common misconception/ignorance around how far websites are able to peer into your private home network. While modern browsers limit this to an extent, it is still overly permissive in my opinion. The privacy implications arise when websites, such as, have the ability to secretly interact with your router’s administrative interface, local services running on your computer and discover devices on your home network. This behavior should be blocked by the same-origin policy (SOP), a fundamental security mechanism built into every web browser since the mid 1990’s, however due to convenience it appears to be disabled for these requests. This caught a lot of people by surprise, including myself, and is why I wanted to make this type of traffic “opt-in” on my devices.

Do you consider port scanning “malware”? 

ACK-J: I don’t necessarily consider port scanning malware, port scanning is commonplace and should be expected for any computer connected to the internet with a public IP address. On the other hand, devices on our home networks do not have public IP addresses and instead are protected from this scanning due to a technology called network address translation (NAT). Due to the nature of how browsers and websites work, the website code needs to be rendered on the user’s device (behind the protections put in place by NAT). This means websites are in a privileged position to communicate with devices on your home network (e.g. IOT devices, routers, TVs, etc.). There are certainly legitimate use cases for port scanning even on internal networks, the most common being communicating with a program running on your PC such as Discord. I prefer to be able to explicitly allow this type of behavior instead of leaving it wide open by default.

Is there a way to summarize how your extension addresses the privacy leak of port scanning?

ACK-J: Port Authority acts in a similar manner to a bouncer at a bar, whenever your computer tries to make a request, Port Authority will verify that the request is not trying to port scan your private network. If the request passes the check it is allowed in and everything functions as normal. If it fails the request is dropped. This all happens in a matter of milliseconds, but if a request is blocked you will get a notification.

Should Port Authority users expect occasional disruptions using websites that port scan, like eBay?

ACK-J: Nope, I’ve been using it for years along with many friends, family, and 1,000 other daily users. I’ve never received a single report that a website would not allow you to login, check-out, or other expected functionality due to the extension blocking port scans. There are instances where you’d like your browser to communicate with an app on your PC such as Discord, in this case you’ll receive an alert and could add Discord to an allow-list or simply click the “Blocking” toggle to disable blocking temporarily.

Do you see Port Authority growing in terms of a feature set, or do you feel it’s relatively feature complete and your focus is on maintenance/refinement?

ACK-J: I like extensions that serve a specific purpose so I don’t see it growing in features but I’d never say never. I’ve added an allow-list to explicitly permit certain domains to interact with services on your private network. I haven’t enabled this feature on the public extension yet but will soon.

Apart from Port Authority, do you have any plans to develop other extensions?

ACK-J: I actually do! I just finished writing up an extension called MailFail that checks the website you are on for misconfigurations in their email server that would allow someone to spoof emails using their domain. This will be posted soon!

Do you have an intriguing extension development story? Do tell! Maybe your story should appear on this blog. Contact us at amo-featured [at] mozilla [dot] org and let us know a bit about your extension development journey.

5 comments on “Developer Spotlight: Port Authority”

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  1. Michael Segers wrote on

    Good stuff


  2. Thomas Kuchenbecker wrote on

    Hope it woks


  3. Tom kuchenbecker wrote on

    Tom likes it


  4. Kevan Rhead wrote on



  5. Tran wrote on

    First Time I try.


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