Browser Extension Visibility: Why Inventory Changes the Game

Browser extensions occupy a unique spot in your security stack. They're not applications in the traditional sense - they're lightweight, frequently updated, and run inside the browser with access to everything your users do on the web. They also exist in a gray area where users can install them freely, often without IT awareness.

This post is specifically about browser extensions, not application control. Extensions require a different approach than traditional software, and understanding why is key to managing them effectively.

Why browser extensions are different from applications

With traditional applications, you're dealing with executables that run on the endpoint. You have established tools for visibility, you can leverage threat intelligence to block known-bad binaries, and you can make surgical decisions based on real attack data. A threat-informed approach - blocking what attackers actually use - makes sense because the attack surface is well-mapped and the intelligence is mature.

Browser extensions are a different problem:

The update model is invisible. Extensions auto-update through the browser store. A legitimate extension today can push a malicious update tomorrow, and your endpoint tools won't see a new binary - just the same extension ID with a different version.

The threat intelligence is thinner. There's no equivalent of LOLBins or LOLDrivers for extensions. Malicious extensions are often net-new, short-lived, or compromised versions of previously legitimate tools. You can't rely on blocklists the same way.

The install path bypasses IT. Users can install extensions with a click. There's no MSI, no deployment tool, no approval workflow by default. Extensions accumulate organically.

Permissions are broad and opaque. An extension with "read and change all your data on websites you visit" has effectively full access to the browser session - credentials, tokens, form data, everything.

Because of these differences, the starting point for extensions isn't "what should we block?" It's "what do we even have?"

Inventory is the foundation

You can't make good decisions about extensions without visibility. And with extensions, visibility is harder than it looks:

• Extensions vary per user, per browser, and per profile (work vs. personal).
• The same extension can be installed multiple ways (user install, policy push, sideload, developer mode).
• Names are meaningless—"PDF Helper" could be legitimate or malicious. What matters is the extension ID, permissions, and behavior.

A strong extension inventory answers:

• What's installed? (extension ID, name, version)
• Where? (which browser, which user, which profile)
• How did it get there? (policy, user, sideload, developer mode)
• What can it access? (permissions and host permissions)
• Is it changing? (version drift, manifest changes)

MagicSword inventories extensions across Chrome, Edge, and Firefox automatically - including multi-profile scenarios. You get fleet-wide visibility without agents phoning home extension-by-extension.

Once you can see what's actually present, you can start asking better questions: Which extensions are most prevalent? Which have the broadest permissions? Which appeared recently? Which are sideloaded or in developer mode?

The threat landscape: what's actually happening

Inventory isn't just hygiene - it's how you catch real attacks. Recent campaigns show a pattern that keeps repeating:

• Legit extensions get bought, updated, or compromised and then pushed to existing users as a "normal" update.
• Permissions are broad ("read and change data on websites you visit", "access tabs", "access clipboard") and users click through prompts.
• Detection is hard because the extension store listing looks normal, ratings can be high, and malicious behavior can arrive later.

A few examples worth noting:

Malicious Chrome extension campaigns at massive scale. GitLab Threat Intelligence documented a campaign involving 16 malicious Chrome extensions impacting 3.2M+ users, including techniques like degrading site security controls and enabling injected payloads. See: GitLab Security Tech Notes (Feb 2025).

Long-running "turn malicious later" campaigns. Reporting described "ShadyPanda," where extensions behaved normally for long periods, gained trust and installs, and then delivered malicious updates across Chrome/Edge user bases. See: The Register (Dec 2025).

Supply chain compromise via developer phishing. A documented incident showed how attackers targeted an extension developer workflow to ship a malicious update that exfiltrated cookies and auth tokens. See: Obsidian Security (Cyberhaven incident, Dec 2024).

The takeaway: you can't rely on store vetting, brand recognition, or user judgment. You need visibility and control.

From visibility to control

Once you have inventory, you can make informed decisions about control. The right level of control depends on your environment, your risk tolerance, and your operational capacity.

Some organizations want tight control. They use browser enterprise policies to restrict extension installs entirely, then explicitly approve a shortlist. This works well for high-security environments or regulated industries where the browser is a controlled tool, not a personal workspace.

Others want visibility with selective enforcement. They inventory everything, monitor for high-risk patterns (broad permissions, sideloads, rapid spread), and intervene when something looks wrong. This works for environments where user productivity and autonomy matter.

Most land somewhere in between. They might block known-bad categories (crypto miners, ad injectors), require approval for extensions requesting sensitive permissions, and allow low-risk extensions freely.

MagicSword supports all of these models. You can:

• Inventory only - See what's installed, track changes, and investigate when needed.
• Enforce per-browser policies - Block or allow specific extensions across Chrome, Edge, and Firefox from a central control plane.
• Layer controls - Combine inventory with selective enforcement based on your risk model.

The key is that control follows from visibility. You're not guessing which extensions to block - you're making decisions based on what's actually present and what risk it represents.

A practical approach to extension management

If you're starting from zero, here's a pragmatic path:

Start with inventory. Turn on extension visibility across your fleet. Don't change anything yet—just observe. Give it a week or two to populate.

Identify your baseline. What are the most common extensions? Which ones have the broadest permissions? Are there sideloaded extensions or developer-mode installs that shouldn't exist?

Flag anomalies. Look for extensions with suspicious patterns: very broad host permissions, recent installs that spread quickly, unknown publishers, or extensions that don't match a clear business need.

Decide on your control posture. Based on what you see, decide how much control you need. Maybe it's just monitoring. Maybe it's blocking a few high-risk categories. Maybe it's a full approval workflow. Let your inventory inform the decision.

Monitor for drift. Extensions change. New ones appear. Existing ones update. Build a habit of reviewing extension inventory periodically - not as a one-time project, but as ongoing hygiene.

Closing: extensions deserve their own strategy

Browser extensions aren't applications, and they shouldn't be managed the same way. They update invisibly, install without oversight, and run with broad access to user sessions. The threat model is different, and the control model should be too.

The foundation is visibility. Once you can see what's installed across your fleet - across browsers, users, and profiles - you can make informed decisions about how much control you need.

MagicSword gives you that visibility out of the box, plus the enforcement controls to act on it when you're ready.

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