Looks like Firefox is immune.

This works by looking for web accessible resources that are provided by the extensions. For Chrome, these are are available in a webpage via the URL chrome-extension://[PACKAGE ID]/[PATH] https://developer.chrome.com/docs/extensions/reference/manif...

On Firefox, web accessible resources are available at "moz-extension://<extension-UUID>/myfile.png" <extension-UUID> is not your extension's ID. This ID is randomly generated for every browser instance. This prevents websites from fingerprinting a browser by examining the extensions it has installed. https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...

• rchaud

  today at 9:24 PM

  And they said that using a browser with sub-5% market share would cause us to miss out on the latest and greatest in web technology!

  • dana321

    today at 9:27 PM

    chrome was made by ex-firefox devs, chrome is still not as good!

• awesome_dude

  today at 9:23 PM

  This is probably a naive question, but...

  Doesn't the idea of swapping extension specific IDs to your browser specific extension IDs mean that instead of your browser being identifiable, you become identifiable?

  I mean, it goes from "Oh they have X, Y , and Z installed" to "Oh, it's jim bob, only he has that unique set of IDs for extensions"

  • triceratops

    today at 9:26 PM

    It's not a naive question. This comment says it's not possible to do that: https://news.ycombinator.com/item?id=46905213

    • awesome_dude

      today at 9:28 PM

      Oh, it's (re)randomised upon each restart, whew, thanks for the heads up

      edit: er, I think that that also suggests that I need to restart firefox more often...

      • tech234a

        today at 10:19 PM

        The webpage would have to scan the entire UUID space to create this fingerprint, which seems unlikely.

        • throwaway808081

          today at 10:41 PM

          Just have a database of UUIDs. Seems pretty trivial to generate and sort as it's only 16 bytes each.

        • today at 10:22 PM

  • b112

    today at 9:28 PM

    Maybe, but how long are the extension ids? And if they are random, how long to scan a trillion random alphanumeric ids, to find matches?

    I presume the extension knows when it wants to access resources of its own. But random javascript, doesn't.

    • maples37

      today at 9:35 PM

      The extension IDs are UUIDs/GUIDs, so 128 bits of entropy. No site is going to be able to successfully scan that full range.

      • b112

        today at 9:56 PM

        ChatGPT told me it can be done though.

        It won't disclose how, as it says it has had several users report it. And that it expects 50% of the bounty, and will use it for GPU upgrades.

    • today at 10:26 PM

    • today at 9:41 PM

  • today at 9:28 PM

Skimming the list, looks like most extensions are for scraping or automating LinkedIn usage. Not surprising as there's money to be made with LinkedIn data. Scraping was a problem when I worked there, the abuse teams built some reasonably sophisticated detection & prevention, and it was a constant battle.

• cxr

  today at 9:13 PM

  In order to create the data source that LinkedIn's extension-fingerprinting relies on to work, someone (at LinkedIn*?) almost certainly violated the Chrome Web Store TOS—by (perversely*) scraping it.

  * if LinkedIn didn't get it from an existing data source

• bryanrasmussen

  today at 8:38 PM

  from the code doesn't look like they do anything if they have a match, they just save all the results to a csv for fingerprinting?

  • cxr

    today at 9:25 PM

    "The code" here you're referring to (fetch_extension_names.js[1]) isn't and doesn't claim to be LinkedIn's fingerprinting code. It's a scraper that the researcher behind this repo wrote themselves in order to create the CSV of the data that they're publishing.

    LinkedIn's fingerprinting code, as the README explains, is found in fingerprint.js[2], which embeds a big JSON literal with the IDs of the extensions it probes for. (Sickeningly enough, this data starts about two-thirds of the way through the file* and isn't the culprit behind the bulk of its 2.15 MB size…)

    * On line 34394; the one starting:

        const r = [{
                    id: "aacbpggdjcblgnmgjgpkpddliddineni",
                    file: "sidebar.html"
    

    1. <https://github.com/mdp/linkedin-extension-fingerprinting/blo...>

    2. <https://github.com/mdp/linkedin-extension-fingerprinting/blo...>

• winddude

  today at 9:22 PM

  a problem for linkedin != "a problem". The real problem for people is the back room data brokering linkedin and others do.

• hsbauauvhabzb

  today at 8:30 PM

  Wont someone think of poor little LinkedIn, a subsidiary of one of the largest data brokers in the world?

  • charcircuit

    today at 8:33 PM

    Why frame what you are trying to say like that? Businesses of all sizes deserve the ability to protect their businesses from abuse.

    • jmward01

      today at 9:00 PM

      Do they respect my data? Why do they get to track me across sites when I clearly don't want them to but someone can't scrape their data when they don't want them to. Why should big companies get the pass but individuals not? They clearly consider internet traffic fair game and are invasive and abusive about it so it is not only fair to be invasive and abusive back, it is self defense at this point.

      • hsbauauvhabzb

        today at 9:14 PM

        They don’t need to track your web browser when they’re owned by Microsoft, because they track every action at a lower level.

        • missingdays

          today at 9:20 PM

          What lower level? Microsoft owns internet?

          • zelphirkalt

            today at 9:31 PM

            The operating system. For example see the Windows 11 screenshot debacle/scandal.

      • today at 9:18 PM

    • ronsor

      today at 8:40 PM

      I think they framed it this way because they don't consider scraping abuse (to be fair, neither do I, as long as it doesn't overload the site). Botting accounts for spam is clear abuse, however, so that's fair game.

      • hsbauauvhabzb

        today at 9:12 PM

        No, I consider all data collection and scraping egregious. From that perspective, LinkedIn is hypocritical when Microsoft discloses every filesystem search I do locally to bing.

        • dylan604

          today at 10:14 PM

          Are you not scraping a site with your eyeballs when you view a site?

    • nitwit005

      today at 9:10 PM

      I'm sure there are issues with fake accounts for scraping, but the core issue is that LinkedIn considers the data valuable. LinkedIn wants to be able to sell the data, or access to it at least, and the scrapers undermine that.

      They could stop all the scraping by providing a downloadable data bundle like Wikipedia.

      • compiler-guy

        today at 9:21 PM

        LLMs scrape Wikipedia all the time, or at least attempt to.

        The data bundle doesn't help that at all.

    • sellmesoap

      today at 8:44 PM

      We enjoy the fruits of an LLM or two from time to time, derived from hoards of ill gotten data. Linkedin has the resourses to attempt to block scraping, but even at the resource scale of LI I doubt the effort is effective.

      • charcircuit

        today at 8:55 PM

        I am not denying that scraping is useful. If it wasn't people wouldn't do it. But if the site rules say you aren't allowed to scrape, then I don't think people should be hostile towards the people enforcing the rules.

        • ronsor

          today at 8:57 PM

          Well, they can try to enforce the rules; that's perfectly fair. At the same time, there are many methods of "trying" which I would not consider valid or acceptable ones. "Enforcing the rules" does not give a carte blanche right to snoop and do "whatever's necessary." Sony tried that with their CD rootkits and got multiple lawsuits.

    • b112

      today at 9:33 PM

      Yes, until it becomes abusive and malignly affects innocents.

    • schmidtleonard

      today at 8:43 PM

      The big social media businesses deserve a Teddy Roosevelt character swooping in and busting their trusts, forcing them to play ball with others even if it destroys their moats. Boo hoo! Good riddance. World's tiniest violin.

      This is a popular position across the aisle. Here's hoping the next guy can't be bought, or at least asks for more than a $400M tacky gold ballroom!

  • xp84

    today at 8:34 PM

    I mean, regardless of who they are or even if you don’t like what LinkedIn does themselves with the data people have given them, the random third parties with the extensions don’t additionally deserve to just grab all that data too, do they?

    • josephg

      today at 9:12 PM

      Eh. I worked at a company which made an extension which scraped LinkedIn. We provided a service to recruiters, who would start a hiring process by putting candidates into our system.

      The recruiters all had LinkedIn paid accounts, and could access all of this data on the web. We made a browser extension so they wouldn’t need to do any manual data entry. Recruiters loved the extension because it saved them time.

      I think it was a legitimate use. We were making LinkedIn more useful to some of their actual customers (recruiters) by adding a somewhat cursed api integration via a chrome extension. Forcing recruiters to copy and paste did’t help anyone. Our extension only grabbed content on the page the recruiter had open. It was purely read only and scoped by the user.

    • mathfailure

      today at 8:54 PM

      Surely they do! The data is in the public internets, aren't they?

      • ronsor

        today at 8:54 PM

        They'd put Widevine or PlayReady DRM on the website if they could, I'm sure.

        • bigfishrunning

          today at 9:19 PM

          why can't they?

    • hsbauauvhabzb

      today at 9:53 PM

      I say the same thing about my start menu sending every action I perform to bing.

    • sieabahlpark

      today at 8:45 PM

      [dead]

• dumbo23

  today at 9:26 PM

  [dead]

Looks like this has been known since 2019.

https://www.nymeria.io/blog/linkedins-war-on-email-finder-ex...

I can confirm.. open up linkedIn.. hit F12 and watch the error count keep going up and up and up

Screenshots found here https://x.com/DenisGobo/status/2018334684879438150

• 9021007

  today at 8:33 PM

  xcancel link: https://xcancel.com/DenisGobo/status/2018334684879438150

I wrote a blog post recently about the technique used by LinkedIn to do extension probing, as well as other ways to do it with less side effects

https://blog.castle.io/detecting-browser-extensions-for-bot-...

Chrome is the new IE6. Google set themselves up to be the next Microsoft and is "ad friendly" in all the creepy ways because that's what Google IS an ad company. All they've contributed to security is diminishing the capability of adblockers and letting malware to do bad things to you as consumers.

• 0xbadcafebee

  today at 9:54 PM

  He who controls the Ads, controls the Internet.

• themafia

  today at 9:54 PM

  > Google set themselves up to be the next Microsoft

  Google became a monopoly. All monopolies do this.

I wrote an article about it a couple of months ago. I also explain why, how and a way to prevent it.

https://javascript.plainenglish.io/the-extensions-you-use-ar...

• jmholla

  today at 9:16 PM

  To clarify, you talk about why it's possible, not why LinkedIn is doing it, right? Or did I miss something in your article.

> This repository documents every extension LinkedIn checks for and provides tools to identify them.

I get that the CSV lists the extensions, and the tools are provided in order to show work (mapping IDs to actual software). But how was it determined that LinkedIn checks for extensions with these IDs?

And is this relevant for non-Chrome users?

• usefulposter

  today at 8:42 PM

  Technical writeup from a few weeks ago by a vendor that explains how LinkedIn does it, then boasts that their approach is "quieter, harder to notice, and easier to run at scale":

  https://blog.castle.io/detecting-browser-extensions-for-bot-...

LinkedIn is the worst walled garden of all of them.

Setup a quick CDP connection. Have Claude Code attach and inject JS into Page.addScriptToEvaluateOnNewDocument. Loads before the page.

Typical early hooks: • fetch wrapper • XMLHttpRequest.prototype.open/send wrapper • WebSocket constructor wrapper • history.pushState/replaceState wrapper • EventTarget.addEventListener wrapper (optional, heavy) • MutationObserver for DOM diffs • Error + unhandledrejection capture

• HumanOstrich

  today at 10:09 PM

  This is irrelevant to the article and discussions here. Weird copypasta bullet points too.

• shj2105

  today at 9:22 PM

  what would this do?

Curious question: why would they check for installed extensions on one's browser?

• CobrastanJorji

  today at 9:08 PM

  Fingerprinting. There are a few reasons you'd do it:

  1. Bot prevention. If the bots don't know that you're doing this, you might have a reliable bot detector for a while. The bots will quite possibly have no extensions at all, or even better specific exact combination they always use. Noticing bots means you can block them from scraping your site or spamming your users. If you wanna be very fancy, you could provide fake data or quietly ignore the stuff they create on the site.

  2. Spamming/misuse evasion. Imagine an extension called "Send Messages to everybody with a given job role at this company." LinkedIn would prefer not to allow that, probably because they'd want to sell that feature.

  3. User tracking.

  • xz18r

    today at 10:33 PM

    I wrote some automation scripts that are not triggered via browser extensions (e.g., open all my sales colleagues’ profiles and like their 4 most recent unliked posts to boost their SSI[1], which is probably the most ‘innocent’ of my use-cases). It has random sleep intervals. I’ve done this for years and never faced a ban hammer.

    Wonder if with things like Moltbot taking the scene, a form of “undetectable LinkedIn automation” will start to manifest. At some point they won’t be able to distinguish between a chronically online seller adding 100 people per day with personalized messages, or an AI doing it with the same mannerisms.

    [1] https://business.linkedin.com/sales-solutions/social-selling...

• jppope

  today at 8:24 PM

  most automations for sales and marketing use browser extensions... linkedIn wants you using their tools not 3rd party

  • Nextgrid

    today at 8:25 PM

    Their own tools suck, that’s the issue.

• staticshock

  today at 8:25 PM

  For a social network, more information about their users = better ad targeting. It likely gets plumbed into models to inform user profiles.

  • Aurornis

    today at 8:49 PM

    Look at the actual list. It's primarily questionable AI tools, scrapers, lead generation tools, and other plugins in that vein.

    I would guess this is for rate limiting and abuse detection.

• HPsquared

  today at 8:24 PM

  An attempt at fingerprinting, I suppose?

• today at 8:23 PM

I wonder if this is why the linkedin feed blocker I installed in Firefox 2 weeks ago stopped working for me within 24 hours

So it really is espionage at all levels.

const nameA = getName(a).toLowerCase(); const nameB = getName(b).toLowerCase(); return nameA.localeCompare(nameB);

const msg = createDoneMessage(); msg.style.opacity = '1';

    console.log("Extensions sorted alphabetically!");
    console.table(sortedCards.map(c => ({
        name: getName(c),
        id: c.id || '—'

Another thing... they alter the localStorage & sessionStorage prototype, by wrapping the native ones with a wrapper that prevent keys that not in their whitelist from being set.

You can try this by opening devtools and setting

  localStorage.setItem('hi', 123)

    cut -d',' -f2 chrome_extensions_with_names_all.csv | grep -c "AI"
    474

I suggest everyone take a look at the list of extensions and their names for some very important context: https://github.com/mdp/linkedin-extension-fingerprinting/blo...

I didn't find popular extensions like uBlock or other ad blockers.

The list is full of scammy looking data collection and AI tools, though. Some random names from scrolling through the list:

- LinkedGPT: ChatGPT for LinkedIn

- Apollo Scraper - Extract & Export Apollo B2B Leads

- AI Social Media Assistant

- LinkedIn Engagement Assistant

- LinkedIn Lead Magnet

- LinkedIn Extraction Tool - OutreachSheet

- Highperformr AI - Phone Number and Email Finder

- AI Agent For Jobs

These look like the kind of tools scummy recruiters and sales people use to identify targets for mass spamming. I see several AI auto-application tools in there too.

• NicuCalcea

  today at 10:09 PM

  LinkedIn itself provides tools for scummy recruiters to mass spam, so this is just them protecting their business.

  Also, not all of them are data collection tools. There are ad blockers listed (Hide LinkedIn Ads, SBlock - Super Ad Blocker) and just general extensions (Ground News - Bias Checker, Jigit Studio - Screen Recorder, RealEyes.ai — Detect Deepfakes Across Online Platforms, Airtable Clipper).

See also: a demo page for the same technique that can enumerate many extensions installed in your browser: https://browserleaks.com/chrome

• xnx

  today at 10:05 PM

  Yuck. Disgusting that extension detection is possible.

I’m probably on the list. I made a LinkedIn Redactor that allowed you to add keywords and remove posts from your thread that included such words. It’s the X feature but for LinkedIn. Anyway, got a cease and desist from those lame fucks at LI. So I removed from the chrome store but it’s still available on GitHub.

[removed]

• ronsor

  today at 8:22 PM

  This is a security vulnerability and should be patched. Sorry, LinkedIn.

  (Alternatively extension developers can modify their extensions to block these requests!)

  • 0cf8612b2e1e

    today at 8:24 PM

    No kidding. I am shocked this works.

    Does Firefox have a similar weakness?

    • tech234a

      today at 8:58 PM

      No. Firefox always randomizes the extension ID used for URLs to web accessible resources on each restart [1]. Apparently, manifest v3 extensions on Chromium can now opt into similar behavior [2].

      [1]: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...

      [2]: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...

      • tech234a

        today at 10:26 PM

        An additional improvement added in manifest v3 in both Chromium and Firefox is that extensions can choose to expose web accessible resources to only certain websites. Previously, exposing a web accessible resource always made that resource accessible to all websites.

    • cxr

      today at 8:52 PM

      It doesn't work. The person who posted the comment you're responding to has absolutely no idea what he's talking about. He confabulated the entire explanation based on a single misunderstood block of code that contains the comment «Remove " - Chrome Web Store" suffix if present» in the (local, NodeJS-powered) scraper that the person who's publishing this data themselves used to fetch extension names.

    • burkaman

      today at 8:46 PM

      I don't see any evidence of this happening in Firefox. Either it's more difficult or they just didn't bother, either way I'm happy.

      Edit: Can't find much documentation on exactly how the anti-fingerprinting works, but this page implies that the browser blocks extension detection: https://support.mozilla.org/en-US/kb/trackers-and-scripts-fi...

  • MrGilbert

    today at 8:41 PM

    I'm not sure how you'd patch that. Any request that’s made from the current open tab / window is made on behalf of the user. From my point of view, it's impossible for the browser to know, if the request is legit or not.

    • ronsor

      today at 8:43 PM

      An ideal implementation of the same origin policy would make it impossible for a site (through a fetch call or otherwise) to determine whether an extension resource exists/is installed or the site simply lacks permission to access it.

  • toomuchtodo

    today at 8:25 PM

    Is there no browser setting to defend against this attack? If not, there should be, versus relying on extension authors to configure or enable such a setting.

    • zahlman

      today at 8:44 PM

      I imagine that it would require browsers to treat web requests from JS differently from those initiated by the user, specifically pretending the JS-originating requests are by logged-out or "incognito" users (by, I suppose, simply not forwarding any local credentials along, but maybe there's more to it than that).

      Which would probably wreak havoc with a lot of web apps, at least requiring some kind of same-origin policy. And maybe it messes with OAuth or something. But it does seem at least feasible.

      • circuit10

        today at 9:10 PM

        As people have said it’s not making requests to web store, that’s just part of this repository looking for what extensions it’s blocking via nodejs

        Browsers already have strong protections against that sort of thing, look up the same-origin policy and CORS

        • zahlman

          today at 9:22 PM

          I see, I was too credulous.

• chocolatkey

  today at 8:36 PM

  That’s incorrect, it’s trying to load an asset (hardcoded unique per-extension path) for each extension, there is a huge list of these in the source code: https://raw.githubusercontent.com/mdp/linkedin-extension-fin...

• jsheard

  today at 8:35 PM

  Looks to me like LinkedIn is fetching chrome-extension://{extension id}/{known filename} and seeing if it succeeds, not pinging the web store.

  Should be patched nonetheless though, that's a pretty obscene fingerprinting vector.

  • what

    today at 9:12 PM

    How do you patch it? The extensions themselves (presumably) need to access the same web accessible resources from their content scripts. How do you differentiate between some extension’s content script requesting the resource and LinkedIn requesting it?

    • jsheard

      today at 9:15 PM

      Firefox already mitigates this by randomizing the extension path: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...

          The file is then available using a URL like: moz-extension://<extension-UUID>/images/my-image.png"
          <extension-UUID> is not your extension's ID. This ID is randomly generated for every browser instance.
          This prevents websites from fingerprinting a browser by examining the extensions it has installed.

      • zahlman

        today at 9:21 PM

        Doesn't the browser know which script it's running?

        Why can't it just deny access to the specified path, except to the extension itself?

        • cxr

          today at 9:44 PM

          It does by default, except for the files from the extension that the extension author has explicitly designated as content-accessible. It's explained ("Using web_accessible_resources") at the other end of the link.

• halapro

  today at 8:30 PM

  If this is true, it's insane that this would work:

  - why does CWS respond to cross-site requests?

  - why is chrome sending the credentials (or equivalent) in these requests?

  - why is the button enabled server-side and not via JS? Google must be confident in knowing the exact and latest state of your installed extensions enough to store it on their servers, I guess

  • cxr

    today at 9:00 PM

    It's not true. The person you're responding to has a habit of posting implausible-but-plausibly-plausible nonsense, and it's not how this works at all.

    • lapcat

      today at 9:47 PM

      I made the mistake of trying to skim the code hastily before I had to leave to run an errand, and yes it turns out I was wrong, but please refrain from the personal comments, and no, I don't have any such "habit."

      • cxr

        today at 9:59 PM

        Wrong again. (PS: The fact that you have now replied—which automatically disables comment deletion—is the only thing that prevented my removing it just now. So great job.)

        • lapcat

          today at 10:12 PM

          > The fact that you have now replied—which automatically disables comment deletion—is the only thing that prevented my removing it just now. So great job.

          How was I supposed to know that you intended to delete it?

          In any case, you may still have time to edit your comment, as I did with my erroneous root-level comment, since I can't delete that either, for the same reason.

          • cxr

            today at 10:27 PM

            Not interested. You also shouldn't have done that. You broke the thread—exactly what HN's no-deleting-comments-that-have-replies check was created to prevent.

            Consider this: just stop being reckless.

• cobertos

  today at 8:23 PM

  Wouldn't that mean 2900 requests from fingerprint.js??

  • today at 8:48 PM

• today at 8:57 PM

• usefulposter

  today at 8:34 PM

  Isn't it enumerating web_accessible_resources? Below static collectFeatures(e, t) there is a mapping of extension IDs to files in the const r (Minified JS, obviously.)

  Edit: Confirmed. It's not pinging the Chrome Web Store. https://blog.castle.io/detecting-browser-extensions-for-bot-...

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