Malicious Browser Extensions: The Risks of Fake Add-Ons

Browser extensions in enterprise environments are used by 99% of all employees, with half having at least 10 installed. While these extensions can be used to improve efficiency, there is a growing number of malicious browser extensions that can pose a malware risk for users. These fake browser extensions may look normal, but in reality, they are doing malicious actions behind the scenes.

In this blog we’ll be analyzing malicious browser extensions and how they can have a serious data and malware risk for organizations.

What are Malicious Browser Extensions?

A browser extension is a piece of software that allows you to add a custom function to your browser, such as helping you take notes. While many people within organizations use them to improve efficiency, they can also introduce security risks.

A browser extension can perform a wide range of tasks. It can block ads, store passwords, spell-check, and more. To do all these tasks, they generally need permissions over your browser. This can include viewing every site you visit or even your keystrokes.

Malicious browser extensions are designed to look and function like a legitimate extension, but with the goal of doing something malicious like stealing data. Fake browser extensions may pose a malware risk or contain security flaws that compromise a system.

Even downloading extensions from trusted places such as the Google Chrome Web Store can be risky. There have been instances of malicious browser extensions being downloaded from these platforms. When one is found and deleted, two more fake browser extensions pop up.

(Example of a malicious browser extension)

Photo by Malwarebytes

Malware Risks from Malicious Browser Extensions

Malware can be defined as harmful software that invades or corrupts a system. Its goal is to cause havoc, steal information, sabotage systems, or a combination of the three. Malware risk from fake browser extensions is a rising issue.

Since browser extensions involve software being installed, they can sometimes become a vehicle for malware. Koi researchers found a threat actor that spent years building trusted browser extensions before running malware through updates.

These extensions were able to spy on users, steal browsing data, and run malicious code that affected millions of users. The key risk is that the store doesn’t monitor what extensions do after approval, leaving users vulnerable to attacks.

While browser extensions can pose a malware risk, there are ways of spotting and avoiding malicious browser extensions.

How to Spot Fake Browser Extensions

When it comes to fake browser extensions, there are some ways you can spot them. Here’s what we recommend reviewing when deciding if a browser extension poses a malware risk or not:

• Generic Names: Browser extensions simply labeled as “deal finder” or “ad blocker” with generic names, poor grammar, and vague descriptions are all red flags for a malicious browser extension.
• Bad Reviews and Excessive Permissions: Extensions with poor reviews may indicate either low quality or that the extension is fake. Some browser extensions may also ask for too many permissions. A calculator extension should not be requesting access to your data.
• Stick With Verifiable Sources: While there have been instances of malicious browser extensions in the Chrome Store and other verified ones, these are generally your safest option. Try to find extensions that are labeled as “verified” and stick to names you trust.
• Monitor Your Device: If you notice your device draining more battery, consuming more electricity, or generating excess heat after downloading an extension, you may have installed a malicious browser extension. Some extensions appear normal, but they can be secretly mining cryptocurrency for an attacker, which slows productivity and can shorten your hardware’s lifespan.

While malicious browser extensions can still slip through as we saw with the Koi researchers, following these tips will minimize your exposure to them.

(Clone of a real extension)

Photo by Kaspersky

Reducing Malware Risk from Malicious Browser Extensions

One lesson stands out. Trust is the vulnerability. Malicious browser extensions often appear legitimate, pass initial reviews, and gain user confidence long before they introduce a malware risk. By the time suspicious behavior appears, damage may already be done.

For organizations, this creates a blind spot that traditional anti-virus would miss. With modern cyberattacks being able to access sensitive data, credentials, and web activity while quietly operating in the background, ongoing visibility and control are no longer optional.

Reducing malware risk starts with awareness, clear IT policies, and regular reviews of security across your environment. If you want help understanding and managing cybersecurity risks across your organization, our team is here to take that burden off your shoulders so you can focus on running your business.