Several aspects of browser extensions make them inherently risky. These characteristics make them incredibly useful attack vectors for threat actors.

They can request broad permissions

According to Cybernews, 86% of Chrome extensions demand permissions that could be dangerous in the wrong hands. Another study found that nearly half of extensions request permissions they don't need. Extensions regularly demand wide-ranging API privileges—such as reading clipboard data, monitoring user input on webpages, or modifying network requests. This can grant a malware extension extensive visibility into sensitive business applications.

Users rarely review them after installation

Users rarely review the active extensions they've granted so many permissions to. Once installed, extensions quietly operate in the background. Because it typically runs within an existing browser process (rather than launching a separate executable), browser extension malware is usually less visible than traditional malware, particularly in environments that lack dedicated browser-security controls.

Extensions can update automatically

Browsers are designed to automatically update installed extensions in the background to ensure security patches are applied quickly. This creates a significant supply-chain risk. In one example of Chrome malware extensions, attackers compromised the developer accounts of at least 35 extensions via phishing emails. They then pushed malicious background updates to over 2.5 million users.

Once-legitimate extensions can become malicious

How does malware sneak past Chrome Web Store vetting? Attackers take advantage of automatic updates in sophisticated ways. For example, adversaries acquire well-established extensions or develop helpful extensions themselves, slowly building trust and positive reviews, only to push malicious updates. That was the case with the ShadyPanda Campaign (2024), in which the cybercrime group compromised several trusted browser extensions, turning them into spyware that affected over 4 million users. That attackers are willing to run this "long con" game speaks to how potentially valuable malicious browser extensions can be.

Whether it's Safari, Firefox, or Chrome, browser extension malware can affect users across browsers and operating systems. Here are the top warning signs of malicious extension activity:

Unexpected browser redirects

Malicious extensions often attempt to monetize user traffic or redirect searches. If a browser redirects standard searches through unfamiliar intermediary domains, or if tracking pixels and affiliate codes are injected into shopping URLs, an extension could be manipulating traffic.

Extensions requesting new permissions

While legitimate software updates occasionally require new features, a prompt from an installed, simple extension asking to "read and change all your data on the websites you visit" could be the sign of an ownership change or upstream compromise.

Unfamiliar extensions installed across multiple users

If the same unrecognized extension appears across multiple user profiles, it may indicate silent "sideloading." In these cases, malware running locally on the operating system bypasses the official web store entirely and instead drops extension files directly into the browser's directory, forcing the browser to load the extension. Once present on an endpoint, the malware installer may spread to other users via shared workstations, roaming user profiles, or lateral movement techniques.

Strange login activity with Microsoft 365 and Google Workspace

Malicious extensions can intercept and export active session tokens (cookies), allowing threat actors to bypass MFA by hijacking a user's authentication in cloud applications. If a security team notices successful logins from unfamiliar geographic locations, impossible travel, or unrecognized user-agent strings, it could be a signal that a malware extension has stolen active cookies.

Because of the high risks that malicious browser extensions carry, organizations shouldn't wait for users to notice the obvious signs. Security teams need centralized visibility over all active extensions. Using tools like Chrome Browser Cloud Management or Microsoft Intune, admins can generate complete, real-time inventories of all deployed extensions. They can then remove any unnecessary or unapproved extensions. To immediately remove extensions across a Windows-managed environment, admins can use registry-level controls.

Before approving any extension, security teams should weigh the tool's required permissions against its business utility. For example, if a simple utility like a screen recorder demands access to all web traffic, the organization should look for an alternative.

If a malicious extension is discovered on an endpoint, the incident should be treated as an account compromise. Simply deleting the extension doesn't address the threat of exfiltrated data. Security teams should:

• Isolate the host
• Terminate all active browser processes
• Delete the extension folders from local storage
• Revoke active session tokens and cookies
• Reset passwords for affected accounts
• Re-register MFA factors where appropriate

To guard against malicious browser extensions in the future, IT teams can take several steps:

Create an approved extension list

Malicious extensions are highly dynamic. A safe, trusted extension today could become compromised down the road. Organizations should move from a reactive "blocklist" model to a zero-trust "allowlist-only" model. This approach blocks all extensions by default, allowing only vetted, pre-approved tools.

Limit high-risk permissions

ExtensionSettings policy allows administrators to centrally define granular rules governing which extensions can be installed, force-installed, blocked, or granted specific permissions.

Treat browser extensions like software assets

Browser extensions should be integrated into organizations' software asset management (SAM) tools. This includes maintaining a complete registry of active extensions and monitoring for known vulnerabilities, ownership changes, developer abandonment, and newly requested permissions.

Train users to avoid installing unverified AI or productivity tools

Shadow AI—employees installing unapproved AI tools—is a growing threat across organizations, and threat actors are actively exploiting the rapid adoption of AI productivity tools with browser extensions. While traditional security training focused mainly on link-based email phishing, modern security awareness training should also educate users on extension-based social engineering—especially on AI productivity lures. Adversaries can use browser-based sidebar utilities to harvest chat histories, prompts, and source code submissions from LLMs, potentially putting sensitive data at risk.

Malicious browser extensions are so risky because they operate unseen within browsers. While you can take steps to guard against unapproved extensions, the prevalence of shadow IT suggests that malicious extensions will find a way into your environment. Teams can't assume employees will spot the signs before a serious breach has occurred.

Huntress doesn't manage browser extension allowlists or directly remove extensions, but Huntress Managed EDR and Managed ITDR can help detect and respond when extension abuse turns into endpoint or identity compromise. Learn more and enhance your defenses against this rising threat.