Experts from the antivirus software manufacturer Avast have discovered malware that was hidden in at least 28 dangerous third-party extensions for Google Chrome and Microsoft Edge.All of these extensions were associated with popular platforms: for the Google Chrome browser it was Video Downloader for Facebook, Vimeo Video Downloader, Instagram Story Downloader, VK Unblock, and on the list of specialists are several extensions for the Microsoft Edge browser.
A complete list can be found here.
The detected malware allows extensions to download additional malware to the user’s computer, can redirect victims’ traffic to advertising or phishing sites, steal personal data (for example, birth dates, email addresses) and information about active devices.
Considering the number of downloads of these extensions in app stores, approximately 3,000,000 people could be affected worldwide.
Users also complain that these extensions interfere with their online experience and redirect them to other sites. Each time a user clicked a link, the extensions sent information about this action to the hackers’ C&C server.
“Then an attacker can issue a command to redirect a person from a real link to a new, malicious URL, and only then send him to the site he originally planned to visit”, – say Avast experts.
All this endangers the privacy of users, since the log of all clicks is transferred to third-party intermediary sites. Also, hackers extract and collect dates of birth, email addresses and device information, including the time of the first and last login, device name, operating system, browser used and its version, even IP addresses (can be used to determine the geographic location of the victim) …
Avast researchers believe that the goal of this campaign is primarily to monetize traffic: for each redirect to a third-party domain, cybercriminals receive a payment. Also, extensions can redirect users to advertising or phishing sites.
“We assume that either these extensions were specially created using embedded malware, or the authors waited for the extensions to become popular and then released updates containing malware. It is also possible that the developers sold the original extensions, and the buyer embedded malware in them”, — notes Ian Rubin, malware researcher at Avast.
The Avast Threat Intelligence team began investigating this threat in November 2020, but believes that it could have existed for years, just no one noticed it. There are user reviews on the Chrome store that mention link hijacking, dated December 2018.
“Backdoors in extensions are well hidden, and extensions only start showing malicious activity a few days after installation: this complicates the task for any security solution”, — adds Ian Rubin.
At the moment, all infected extensions are still available for download. Avast contacted the Microsoft and Google Chrome teams and reported the findings. Both Microsoft and Google have confirmed that they are currently investigating this issue.
In the meantime, Avast recommends that users disable or remove extensions temporarily until the problem is resolved, and then scan the PC and remove malware if it is found.
Let me remind you that Edge is moving to a new extension API, but ad blockers will continue to work. What is more, Google allows loose ad blocking policy for Chrome extensions.
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