Browser Extensions: The Silent Insider Threat

Picture this: Your finance team just received an urgent email about updating payment systems. They click a link, install what appears to be a legitimate browser extension to “streamline banking workflows,” and within hours, your company’s financial credentials are silently flowing to cybercriminals halfway around the world. No alarms sound. No security alerts fire. The breach stays invisible for months.

This isn’t a hypothetical scenario — it’s the new reality of browser extension attacks that have exploded across the enterprise landscape.

The Numbers Tell a Startling Story

In the first half of 2025 alone, over 3.2 million users have been compromised through malicious browser extensions, while 722 users were infected with malicious browser extensions in Latin America since early 2025. The scope is staggering: over 100 malicious Chrome extensions have been targeting users worldwide since February 2024, many remaining undetected in Google’s Chrome Web Store for months.

But here’s what should really keep security teams awake at night: Recent industry research shows that nearly all enterprise employees have browser extensions installed, with over half running more than ten extensions. Even more concerning, the majority of enterprise users’ extensions can access sensitive data like cookies, passwords, web page contents, and browsing information.

These aren’t just productivity tools anymore — they’re attack vectors hiding in plain sight.

Why Extensions Have Become the Perfect Attack Vector

Traditional cybersecurity has focused on securing the perimeter, but browser extensions operate inside that perimeter with extraordinary privileges. They can read every webpage you visit, capture every keystroke you type, and access the credentials stored in your browser. Unlike other software, extensions update automatically and silently, meaning a trusted tool can become malicious overnight without any user intervention.

The recent Cyberhaven incident perfectly illustrates this threat. Attackers used spearphishing to compromise developer accounts and pushed malicious updates to extensions used by 400,000 customers. The malicious code was openly available for download in the Google Chrome store for 31 hours, automatically installing on browsers during that window.

What makes this particularly insidious is that most extension publishers are unknown and only identified via basic email accounts, with the majority of publishers having released only one extension. Organizations are essentially trusting anonymous developers with access to their most sensitive data.

The Enterprise Blind Spot

Most enterprises treat browser extensions like office supplies — ubiquitous, barely monitored, and largely ignored by security teams. Traditional endpoint security tools aren’t designed to detect or manage browser activity at this granular level, creating a massive blind spot.

The risk compounds when you consider that many extensions haven’t been updated in over a year, leaving known vulnerabilities unpatched. Meanwhile, a significant portion of enterprise extensions are sideloaded, bypassing even basic store vetting.

This creates what security researchers are calling the “shadow extension” problem — similar to how shadow IT once plagued cloud adoption, unvetted browser extensions now create unmonitored pathways for data exfiltration and system compromise.

The AI Extension Wild West

The explosion of AI-powered extensions has created an entirely new category of risk. A significant portion of enterprise employees use GenAI extensions, with the majority of these having high-risk permission scopes. These extensions often request access to all website data, ostensibly to “enhance” user productivity, but in reality creating perfect conditions for mass data harvesting.

Recent campaigns have specifically targeted trending technologies to increase installation rates, including fake websites impersonating DeepSeek AI following its media attention. Users eager to try new AI tools become unwitting accomplices in their own compromise.

From Blind Spot to Control Point

The good news is that forward-thinking organizations are recognizing this threat and taking action. Modern extension risk management goes far beyond maintaining a blacklist of known-bad plugins. It requires continuous visibility, real-time risk assessment, and policy enforcement that adapts to emerging threats.

Leading solutions now provide complete extension discovery across all browsers and devices, automatic risk scoring based on permissions and publisher reputation, and granular policy controls that can restrict high-risk extensions while preserving productivity tools that employees actually need.

How Acium Turns Extension Chaos Into Security Control

Acium was built specifically to address these challenges. Our platform provides security teams with total visibility into every extension across the organization — including those sideloaded or installed without permission. Each extension is automatically assessed using our proprietary risk engine, which evaluates behavior patterns, permission scopes, publisher reputation, and real-time threat intelligence.

This enables rapid response: flag suspicious extensions before they activate, enforce custom policies based on user roles and risk tolerance, and maintain the delicate balance between security and productivity. Rather than blocking everything, Acium helps organizations make informed decisions about which extensions to trust and which to remove.

The Bottom Line

The era of invisible browser extensions is over. Current research shows that a significant portion of all extensions within an organization pose a high risk, with a smaller but concerning percentage of installed extensions known to be malicious. With the browser becoming the primary workspace for most employees, extension security isn’t just an IT nice-to-have — it’s a business imperative.

The new insider threat doesn’t always come from people. Sometimes it comes from the code running quietly in their browser, trusted implicitly and monitored by no one.

The question isn’t whether your organization will face an extension-based attack. The question is whether you’ll see it coming.

Sources

1. GitLab Security Tech Notes. “Malicious browser extensions impacting at least 3.2 million users.” February 2025.
2. The Hacker News. “Malicious Browser Extensions Infect Over 700 Users Across Latin America Since Early 2025.” June 2025.
3. Spin.AI. “Malicious Browser Extensions Are Security Threats.” March 2025.
4. Field Effect Security Intelligence. “33 Chrome extensions found to be malicious.” January 2025.
5. LayerX Security. “Enterprise Browser Extension Security Report 2025.” April 2025.
6. The Hacker News. “The 2024 Browser Security Report Uncovers How Every Web Session Could be a Security Minefield.” May 2024.
7. Cybernews. “25 Chrome extensions with over 2M users breached: hackers are after user data.” December 2024.
8. CyberSecurity News. “100+ Malicious Chrome Extensions Attacking Users to Exfiltrate Login Credentials & Execute Remote Code.” May 2025.
9. Fox News. “16 hijacked browser extensions expose 3.2 million users.” March 2025.
10. BleepingComputer. “Majority of Browser Extensions Pose Critical Security Risk, A New Report Reveals.” May 2025.