First variant masquerades as Mozilla’s WebExtension browser API Polyfill.I couldn’t find any other extension using the same code as PDF Toolbox, but the two variants I discovered now are very similar.

There is a detailed discussion of the malicious code in my previous article. It’s based on a sample of roughly 1,600 extensions that I have locally, not all the Chrome Web Store contents. Note that this list is unlikely to be complete. These eight extensions are considerably different from the rest, so I published a follow-up blog post discussing the technical aspects here. Update (): Google removed one more extension, so only eight extensions remain now. Right now, only nine extensions from this list remain in Chrome Web Store, and these will hopefully also be dealt with soon. By the time I published my previous update, a bunch of the extensions mentioned there were already gone. Update (): Good news: Google started removing these extensions. So now we are at 34 malicious extensions and 87 million users. With his help I was able to identify yet another variant of this malicious code and a bunch more malicious extensions. Also, Lukas Andersson did some research into manipulated extension ratings in Chrome Web Store and pointed out that other extensions exhibited similar patterns in their review. Update (): With an increased sample I was able to find some more extensions. The most popular of these extensions are Autoskip for Youtube, Crystal Ad block and Brisk VPN: nine, six and five million users respectively. So now we are at 18 malicious extensions with a combined user count of 55 million. And I found more extensions in Chrome Web Store which are using it. I checked it out and found two other versions of the same malicious code. It even gained a considerable number of users after I published my article.Ī reader tipped me off however that the Zoom Plus extension also makes a request to serasearchtopcom. Despite reporting the issue to Google via two different channels, the extension remains online. Two weeks ago I wrote about the PDF Toolbox extension containing obfuscated malicious code.

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