A group of researchers has discovered that malicious code can easily bypass Chrome Extension Security Feature, the team has found a new social engineering trick that leads users to a malicious extension from Google Chrome impersonating to deliver Adobe’s Flash Player to lure victims in a click fraud campaign.According to the experts at TrendMicro the attack starts when victims click on Facebook or Twitter shortened links, the links point to websites that automatically serve the malicious browser extension.Researchers uncovered a baiting tweet that advertises “Facebook Secrets”, claiming to show videos that aren’t publicly available on the Internet.

“We came across one particular post on Twitter that advertises “Facebook Secrets,” along with a shortened link. Clicking the link leads the user to a site that automatically downloads an .EXE file into the user’s system.
This downloaded file, download-video.exe, is actually a downloader malware, which we detect as TROJ_DLOADE.DND. This starts a chain of downloaded and dropped files into the system. In order to avoid suspicion, these files use legitimate-sounding file names like flash.exe.” states a post post.

To evade the security mechanism in Chrome designed to allow extension installations only from the Chrome Web Store the malware created a folder in the browser’s directory where it save the “browser extension components.”

The browser extension components added to Chrome’s extension folder are the following:

• manifest.json – contains browser extension description (name, script to load, version, etc.)
• crx-to-exe-convert.txt– contains the script to be loaded, which can be updated anytime by connecting to a specific URL

Once the browser parses the manifest.json the extension is ready to work. Once the Chrome extension is installed it opens a specific site in the background that is written in Turkish, which is likely used by threat actors for the click fraud or redirection scheme.

Pierluigi Paganini

(Security Affairs – Chrome extension, malware)