Rogue Chrome, Firefox Extensions Hijack Browsers; Prevent Easy Removal

Any malware that hijacks your browser to serve up ads or to redirect you to random websites can be annoying. Even more so are extensions that take control of your browser and prevent you from landing on pages that can help you get rid of them.

Security researchers at Malwarebytes recently discovered extensions for Chrome and Firefox that display precisely that behavior. According to the security vendor, the extensions are designed to hijack browsers and then block users from removing them by closing out pages with information on extensions and add-ons, or by steering users to pages where extensions aren't listed. Rogue extensions like these are often an overlooked attack vector that can leave organizations exposed to serious threats.

News of the rogue extensions follows a report from the ICEBRG Security Research team just this week about several malicious Chrome extensions in Google's Chrome store that has impacted some 500,000 users around the world, including many organizations.

"The Chrome extension is a one-of-a-kind so far," says Pieter Arntz, malware intelligence researcher at Malwarebytes. The code that forces the extension to install on a victim's browser itself looks re-used from another family of forced extensions, he says. "But the code to take users away from the extensions list in Chrome, I've never seen before."

The Firefox extension was a first as well when Malwarebytes initially spotted it, Arntz says. But researchers have already spotted a second version of it since then, he said.

The Chrome extension seems targeted at a specific demographic since it is in Spanish and promises to give users the weather in Colombia. But when installed, it opens a minimized Chrome window to the side of the screen that then accesses dozens of YouTube videos every minute, Arntz says. "So, we assume it was designed to quickly drive up the number of views for those videos." The extension has been around for several weeks and is available in the Chrome Web Store, he notes.

The Firefox extensions meanwhile are being pushed by cryptocurency faucets and similar websites that reward visitors with free content or other incentives for completing tasks like watching ads or completing captchas.

One of the ways users can be trapped into doing forced installs of malicious browsers is by landing on websites designed solely for that purpose. Users can often end up on these sites via redirects from adult, keygen, and software cracking sites, according to Malwarebytes.

"What we call a forced install is that when a website is designed to keep the user there until he decides to install the extension," Arntz says. Such websites employ javascripts, login prompts and various HTML5 tricks to essentially lock down the browser and prevent a user from browsing to another site or even closing down the tab until the extension is installed.

Chrome users have an easier time escaping such sites, by simply opening a new tab and then shutting down the offending tab, while Firefox users can only close them out via the TaskManager.

However, compared to Chrome users, Firefox users can disable the rogue extension more easily once it is actually installed simply by running the browser in Safe Mode, Arntz says. Firefox's Safe Mode allows users to see a list of all browser extensions, even when the extensions are not active, making it relatively simply to uninstall unwanted ones. Chrome in contrast, does not allow users to see any installed extensions when it is started with the extensions disabled.

"In Chrome, you will have to figure out the name of the extension folder and make some significant change there before you can access the list of extensions. Chrome not showing the extensions when you start it with the extensions disabled [has] a big handicap there," Arntz says.

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