Browser extensions sit in a privileged spot. They live inside the browser that your employees already use to access email, SaaS, finance systems, and internal tools. That makes them great for productivity and also perfect for abuse.

The problem is not extensions in general. It is extensions that ask for more power than they need and then hold that power for months or years. That is what "excessive permissions" means: an extension is over‑privileged when it gets broader site or API access than its function really requires. In practice this looks like "read and change all your data on all websites," or access to cookies, history, downloads, or native apps on the endpoint.

When those permissions are misused, you get silent data theft, session hijacking, fraud, and long‑lived persistence with almost no obvious symptom to the user.

Understanding the risk

In a typical company, users install their own extensions to fill gaps: password managers, note‑taking tools, ad blockers, AI helpers. Each one can ask for wide host access, such as all sites, and powerful APIs. Over time, a single browser profile may accumulate dozens of extensions with overlapping rights over the same critical SaaS applications.

Excessive permissions are dangerous because they flatten the boundary between "the user" and "the extension." From the SaaS platform’s point of view, the extension is the user. If the extension reads an inbox, downloads source code from a repository, or forwards cookies to an attacker, it all happens inside a legitimate, authenticated session.

This sits alongside more familiar browser threats like phishing and drive‑by downloads, but it behaves differently. The code is installed from an official store, signed, versioned, and updated through normal channels. Malicious or compromised extensions often remain available for months, sometimes years, and accumulate hundreds of thousands or millions of installs before anyone notices.

Attackers exploit this in three main ways. They publish outright malicious extensions that promise some utility. They compromise legitimate extensions through the supply chain and push a backdoored update. Or they install a hidden extension after gaining endpoint access and use it as a stable foothold into web apps.

How excessive permissions exploits browser architecture

Modern browsers give extensions a structured way to declare what they want to do. They ask for host permissions such as access to specific domains or all URLs. They ask for API permissions like tabs, cookies, scripting, history, downloads, and network rule engines.

Once granted, those permissions let the extension:

• Read and modify page content across the allowed sites. That includes emails, chat logs, dashboards, documents, and anything else in the DOM.
• Manipulate network requests within its scope. Ad blockers use this to remove ads. Attackers can use the same capability to redirect traffic, alter API calls, or inject content.
• Access session cookies. With cookie permission and broad host access, an extension can harvest authentication tokens and impersonate users without needing passwords.
• Talk to local programs via native messaging. That opens a bridge from the browser to the underlying OS for persistence, lateral movement, or deeper data theft.

Real incidents show how this plays out. Mail‑stealing extensions have been used in targeted campaigns to siphon Gmail content from already logged‑in sessions. Supply‑chain compromises have turned popular productivity extensions into data exfiltration tools for a day or two, enough to impact millions of installations before removal. Malware like ViperSoftX installs its own extension with full page access, then quietly alters cryptocurrency transactions inside the browser.

Platform changes like Manifest V3 and bans on remotely hosted code close some doors, but none of them fix the core problem: once an extension has broad, legitimate permissions, it can do almost anything the user can do in the browser.

Why traditional defenses fall short

Most enterprise controls were built around processes, files, and networks. Extensions live in a different layer.

To an endpoint tool, a malicious extension is just more activity from chrome.exe or msedge.exe. Browsing to an attacker’s server looks like any other HTTPS request. No new binary appears on disk. No suspicious process tree emerges. The activity blends into the baseline.

Network tools see encrypted browser traffic leaving for some domain. Unless you are inspecting content deeply and correlating it with extension installs and updates, it looks like ordinary web use.

Data loss prevention tools also struggle because the exfiltration often happens inside the web session itself. The extension reads page content from a SaaS app and posts it out over HTTPS, all within the browser’s process. From the outside, there is no file copy, no USB activity, no email with attachments leaving the company.

Even when vendors provide alerts for known‑bad extensions, they trigger after the fact. A backdoored update can run for hours or days, harvest cookies or data, and then be pulled from the store. Unless you have your own inventory and policy, you may only learn about it from a vendor blog after the damage is done.

Organizational blind spots and human factors

Technology is only half the story. People help make excessive permissions a structural problem.

Most users treat extension stores the way they treat phone app stores. If it is in the store and has many five‑star reviews, it must be safe. Permission prompts are confusing, so users click through them. The sentence "read and change all your data on the websites you visit" is abstract. The productivity benefit is concrete.

Security teams often do not have a complete list of extensions running across the fleet, let alone what each one can access. Remote and BYOD setups make this worse. An employee logs into corporate SaaS from a personal browser with a stack of unknown extensions. None of that is visible to your conventional asset inventory.

There is also ownership drift. An extension that was benign when first approved can change hands or add partners. A later update introduces aggressive tracking or outright malicious code, but the name and icon look familiar, so trust persists.

These human and organizational gaps turn excessive permissions from a one‑off misconfiguration into a long‑term, low‑noise vulnerability across the company.

Strategies for defense

Defending against excessive permissions means treating extensions as software you own, not as harmless personal tweaks.

At a policy level, you want least functionality. Rather than allow everything and block a few obvious abuses, you block by default and allow by exception. Every approved extension should have a reason to exist and a defined set of sites and APIs it is allowed to touch.

During review, look at more than the feature. Check who publishes it, how often it updates, and what permissions it requests. Be skeptical of any extension that wants access to all sites plus cookies or scripting but claims to solve a narrow problem on a single site.

Use browser controls to scope permissions where possible. Favor extensions that rely on optional permissions and "on click" access to specific sites. Avoid native messaging unless there is a clear, documented need. Prefer extensions that already support Manifest V3 and avoid loading remote code.

Finally, build extension review and cleanup into regular security hygiene. Remove unused add‑ons. Revisit older approvals when an extension changes its permissions or ownership or stops updating.

The role of enterprise browsers

Consumer browsers provide base mechanisms, but they are not designed to manage extension risk at enterprise scale. That is where enterprise browser builds and management frameworks help.

Centralized management lets you see, in one place, which extensions are installed on which devices, what versions they run, and what permissions they hold. You can enforce allowlists so that only vetted IDs are installable, and you can force‑install a small set that you have fully reviewed.

Fine‑grained policies let you say "this extension is allowed, but only on these domains, without cookie access, and only above this minimum version." When a new update requests broader permissions, you can hold it back until it is analyzed.

On the detection side, managed browsers can feed extension events and configuration into your security tooling. You can correlate a sudden install or permission change with new outbound connections or suspicious SaaS activity.

The goal is not to ban extensions. It is to keep their useful parts while stripping away the unnecessary power that turns them into a good attack vector.

Practical steps for immediate risk reduction

If you need to reduce risk quickly, start with three moves.

First, inventory and visibility. Use your browser management tools to pull a list of all extensions, grouped by install count and permission scope. Identify anything that has access to all sites plus cookies, history, or scripting.

Second, set a default policy. Block new extensions by default and create a simple request process for exceptions. For the most sensitive groups, allow only a short, known list and remove everything else.

Third, cut obvious overreach. Remove unused extensions, especially from admin and finance accounts. For the rest, reduce host access where possible so they do not run on every site by default.

The path forward

The browser is now the main client for most critical systems. That makes extension governance part of core security, not a side issue.

Excessive permissions turn small bits of convenience code into broad, durable access channels. As more work moves into SaaS and more people work from anywhere on mixed devices, those channels reach deeper into your environment.

Defending against this means building a security architecture that treats extensions as first‑class assets: governed, monitored, and constrained by design. Enterprise browsers and strong extension policies let you keep the productivity benefits while shrinking the blast radius of any single compromise.

Attackers will keep looking for the easiest way to live inside your users’ sessions. If you control extension permissions with the same rigor you apply to admin rights and network access, the browser stays a tool instead of a liability.

FAQ

What are excessive permissions in browser extensions?

Excessive permissions occur when browser extensions ask for more power than they actually need to function. This typically looks like extensions requesting "read and change all your data on all websites" or access to cookies, history, downloads, or native apps on the endpoint. The problem isn't extensions themselves, but extensions that hold these broad permissions for months or years, creating unnecessary security risks.

Why are excessive extension permissions particularly dangerous for businesses?

Excessive permissions flatten the boundary between "the user" and "the extension" from a SaaS platform's perspective. When an extension reads an inbox, downloads source code, or forwards cookies to an attacker, it all happens inside a legitimate, authenticated session. This makes malicious activity nearly invisible to traditional security tools, as it appears as normal user behavior within already-authenticated sessions.

Why don't traditional enterprise security tools effectively detect malicious extension activity?

Traditional security tools struggle because extensions operate within the browser process itself. To endpoint tools, malicious extension activity just looks like normal chrome.exe or browser activity. Network tools see standard encrypted HTTPS traffic. Data exfiltration happens within web sessions rather than through obvious file transfers or email attachments, making it blend into normal baseline activity and avoiding detection by conventional monitoring systems.

What makes Island's approach to browser extension security different?

Island provides enterprise browser management that offers centralized visibility into all extensions across devices, including their versions and permissions. It enables fine-grained policies that allow administrators to specify which extensions can run on which domains, without certain permissions like cookie access, and above minimum versions. Island can also feed extension events into security tooling for correlation with suspicious activity.

What immediate steps can organizations take to reduce extension-related risks?

Start with three key moves: First, inventory all extensions using browser management tools, focusing on those with access to all sites plus cookies, history, or scripting. Second, implement a default-block policy for new extensions with a simple exception request process. Third, remove unused extensions (especially from admin and finance accounts) and reduce host access permissions so extensions don't run on every site by default.