Droidclub Botnet via Malicious Chrome Extensions That Affect More Than Half a Million Users

Security researchers from Trend Micro detected a new botnet dubbed Droidclub distributed through malicious chrome extensions. Attackers used malvertising and social engineering methods to display fake messages that trick’s users into installing the malicious extensions.

More than 423,992 users have been affected with the bot and a total of 89 extensions removed from chrome web store. With Its persistence nature, it makes more difficult for users in Uninstalling or reporting the extension.

Droidclub Execution Flow

It injects ads and cryptocurrency mining scripts to every page the user visiting and it can also modify the contents of the websites, ads by matching the IFRAME sizes.

“Droidclub also abuses legitimate session replay libraries to violate the user’s privacy. These libraries are meant to be used to replay a user’s visit to a website, so that the site owner can see what the user saw, and what he entered into the machine, among other things”, researchers said.

Botnet distributed via malvertising and social engineering methods, if the extension installed it checks with C&C server and installs additional configuration codes.

The infected browser pops up and displays ads periodically, and the frequency of displaying ads controlled by C&C server. Trend Micro published a technical analysis report on Botner behavior.

Also Read Four Chrome Extensions Impacted More than Half a Million Users

It also capable of injecting Javascript library from Yandex Metrica of pages visited by users and modifies certain external links based on the keywords. The malicious extensions reported to Google by Trend Micro and they are disabled now.

“The combination of the extension and the library can steal data entered into forms such as names, credit card numbers, CVV numbers, email addresses, and phone numbers. The library does not capture passwords by design, so these are not stolen by the threat actors”, researchers said.

Botnet Nature and Mitigation – Malicious Chrome Extensions

It is difficult to remove and report the malicious chrome extensions. It blocks the users in reporting the extension by checkings the URL and redirects to extension page.

If users try to uninstall the malicious chrome extensions chrome://extensions/ it redirects to a fake page to believe it is removed, but it remains in the system.

By using Ad blockers and script blockers that can block malicious sites from displaying ads. System administrators can define chrome policies to avoid installing these extensions.