uMatrix has an unfixed vulnerability: here is a workaround

Martin Brinkmann
Jul 15, 2021

Raymond Hill's uBlock Origin and uMatrix browser extensions are popular content blockers. While uBlock Origin is maintained actively by Hill, uMatrix development ended in 2020. A fork, nMatrix, designed for the Pale Moon browser, is still maintained.

The uMatrix browser extension is still in use. Google's Chrome Web Store, on which it is still listed, reveals that it has more than 100,000 users, a figure that can be higher as Google does not echo total number of users to the public. The Firefox extension, for which I wrote a guide in 2017, has more than 29,000 users at the time of writing.

A security researcher discovered a vulnerability in all three extensions. The vulnerability exploits code used by the extensions strict blocking feature. Strict blocking prevents all connections to resources that match the filter. Default installations of the extensions use filter lists that include strict blocking filters.

An attacker may exploit the vulnerability to get the extension to crash or cause memory exhaustion according to the researcher. When the extension crashes, users are left without protection until it is reloaded.

It requires that users become active, e.g. by clicking on a link.

The strict-blocking warning page is only displayed when direct navigations are blocked. This means that malicious hosts would need to induce users to trigger a navigation somehow, such as by clicking a link. iframes are classified as sub-documents and do not trigger the warning page, which should make it harder for malicious hosts to exploit this vulnerability in the background.

The researcher tested a proof of concept vulnerability against Chrome, Firefox and Pale Moon. Only the Chrome extension crashed during tests.

Raymond Hill was notified before the security issue was disclosed publicly, and a fix was created for uBlock Origin within one day and published the next. The maintainer of nMatrix published an update to the Pale Moon add-ons site that fixed the issue in the extension as well.

The uMatrix extension is not maintained anymore, which means that it is still vulnerable and will remain so.

How to mitigate the vulnerability

The researcher notes that users need to disable all filter lists on the "assets" tab of the uMatrix dashboard. Subscribing to malware or multi-purpose filter lists may reduce the impact the change has on the blocking of the extension.

To mitigate the vulnerability for now, users can disable uMatrix’s strict-blocking support by unselecting all of the filter lists on the "Assets" tab in the uMatrix dashboard. They can also enable all of the "Malware domains" and "Multipurpose" filter lists in uBlock Origin to help offset the lost filtering coverage.

Closing Words

With development having ended some time ago, it may be time to move to a different extension for content blocking, especially since it has an unpatched vulnerability now. While it seems unlikely that it is going to be exploited in large scale attacks, it is still something that users need to be aware of.

Now You: are you still using uMatrix? (thank you Marcus [via Email])

uMatrix has an unfixed vulnerability: here is a workaround
Article Name
uMatrix has an unfixed vulnerability: here is a workaround
A vulnerability was disclosed recently that affects the discontinued but still popular browser extension uMatrix. A workaround is available!
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  1. ilev said on August 4, 2012 at 7:53 pm

    Doesn’t Windows 8 know that www. or http:// are passe ?

    1. Martin Brinkmann said on August 4, 2012 at 7:57 pm

      Well it is a bit difficulty to distinguish between domains and files for instance.

    2. Leonidas Burton said on September 4, 2023 at 4:51 am

      I know a service made by google that is similar to Google bookmarks.

  2. VioletMoon said on August 16, 2023 at 5:26 pm

    @Ashwin–Thankful you delighted my comment; who knows how many “gamers” would have disagreed!

  3. Karl said on August 17, 2023 at 10:36 pm


    The comments section under this very article (3 comments) is identical to the comments section found under the following article:

    Not sure what the issue is, but have seen this issue under some other articles recently but did not report it back then.

  4. Anonymous said on August 25, 2023 at 11:44 am

    Omg a badge!!!
    Some tangible reward lmao.

    It sucks that redditors are going to love the fuck out of it too.

  5. Scroogled said on August 25, 2023 at 10:57 pm

    With the cloud, there is no such thing as unlimited storage or privacy. Stop relying on these tech scums. Purchase your own hardware and develop your own solutions.

    1. lollmaoeven said on August 27, 2023 at 6:24 am

      This is a certified reddit cringe moment. Hilarious how the article’s author tries to dress it up like it’s anything more than a png for doing the reddit corporation’s moderation work for free (or for bribes from companies and political groups)

  6. El Duderino said on August 25, 2023 at 11:14 pm

    Almost al unlmited services have a real limit.

    And this comment is written on the dropbox article from August 25, 2023.

  7. John G. said on August 26, 2023 at 1:29 am

    First comment > @ilev said on August 4, 2012 at 7:53 pm

    For the God’s sake, fix the comments soon please! :[

  8. Kalmly said on August 26, 2023 at 4:42 pm

    Yes. Please. Fix the comments.

  9. Kim Schmidt said on September 3, 2023 at 3:42 pm

    With Google Chrome, it’s only been 1,500 for some time now.

    Anyone who wants to force me in such a way into buying something that I can get elsewhere for free will certainly never see a single dime from my side. I don’t even know how stupid their marketing department is to impose these limits on users instead of offering a valuable product to the paying faction. But they don’t. Even if you pay, you get something that is also available for free elsewhere.

    The algorithm has also become less and less savvy in terms of e.g. English/German translations. It used to be that the bot could sort of sense what you were trying to say and put it into different colloquialisms, which was even fun because it was like, “I know what you’re trying to say here, how about…” Now it’s in parts too stupid to translate the simplest sentences correctly, and the suggestions it makes are at times as moronic as those made by Google Translations.

    If this is a deep-learning AI that learns from users’ translations and the phrases they choose most often – which, by the way, is a valuable, moneys worthwhile contribution of every free user to this project: They invest their time and texts, thereby providing the necessary data for the AI to do the thing as nicely as they brag about it in the first place – alas, the more unprofessional users discovered the translator, the worse the language of this deep-learning bot has become, the greater the aggregate of linguistically illiterate users has become, and the worse the language of this deep-learning bot has become, as it now learns the drivel of every Tom, Dick and Harry out there, which is why I now get their Mickey Mouse language as suggestions: the inane language of people who can barely spell the alphabet, it seems.

    And as a thank you for our time and effort in helping them and their AI learn, they’ve lowered the limit from what was once 5,000 to now 1,500…? A big “fuck off” from here for that! Not a brass farthing from me for this attitude and behaviour, not in a hundred years.

  10. Anonymous said on September 28, 2023 at 8:19 am

    When will you put an end to the mess in the comments?

  11. RIP said on September 28, 2023 at 9:36 am

    Ghacks comments have been broken for too long. What article did you see this comment on? Reply below. If we get to 20 different articles we should all stop using the site in protest.

    I posted this on [] so please reply if you see it on a different article.

    1. RIP said on September 28, 2023 at 11:01 am

      Comment redirected me to [] which seems to be the ‘real’ article it is attached to

  12. RIP said on September 28, 2023 at 10:48 am

    Comment redirected me to [] which seems to be the ‘real’ article it is attached to

  13. Mystique said on September 28, 2023 at 12:13 pm

    Article Title: Reddit enforces user activity tracking on site to push advertising revenue
    Article URL:

    No surprises here. This is just the beginning really. I cannot see a valid reason as to why anyone would continue to use the platform anymore when there are enough alternatives fill that void.

  14. justputthispostanywhere said on September 29, 2023 at 3:59 am

    I’m not sure if there is a point in commenting given that comments seem to appear under random posts now, but I’ll try… this comment is for

    My temporary “solution”, if you can call it that, is to use a VPN (Mullvad in my case) to sign up for and access Reddit via a European connection. I’m doing that with pretty much everything now, at least until the rest of the world catches up with GDPR. I don’t think GDPR is a magical privacy solution but it’s at least a first step.

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