How to Audit a browser extension's permissions

Your firm's browsing history is effectively a client list. A paralegal who installs a "PDF merge and annotate" extension to mark up a discovery production is quietly handing a third-party script the same view of that document she has. If the extension can "read and change all your data on all websites," it isn't just annotating PDFs — it can see the case management portal in the next tab, the e-filing session, the client email thread pinned above it. Almost nobody stops to audit a browser extension's permissions before it ends up exactly there.

Most people install extensions the way they click "Accept" on a cookie banner: fast, without reading the fine print. For a lawyer, analyst, or anyone whose browser touches privileged material, that habit is a confidentiality exposure, not a mere inconvenience. A single over-permissioned or quietly compromised extension can read, exfiltrate, or tamper with anything rendered on the page — including anything you've captured for a case file.

This guide shows you how to audit a browser extension's permissions properly: what the free, built-in chrome://extensions review tells you (and where it goes blind), a repeatable process using a risk-scoring tool, a full worked example of a keep/remove/replace decision, and — just as important for professional-services work — how to document the audit itself so you can produce it again later. By the end you'll have a process that takes minutes per extension, not a scramble after a headline.

Why Auditing a Browser Extension's Permissions Is Harder Than It Looks

The instinct is to check permissions once, at install, and move on. That's the first mistake. Extensions update automatically, and a developer can ship a new version with broader scope without any fresh install prompt if the user already granted a compatible permission.

The December 2024 Cyberhaven incident is the textbook case. Attackers compromised a legitimate developer's account through a phishing attack and pushed a malicious update to an extension people had already trusted and already installed — no new install, no new click required. TechCrunch's reporting on the breach found the broader campaign affected roughly 35 Chrome extensions and more than 2.6 million users, all through the same supply-chain path: a trusted update channel, not a suspicious new download.

The second mistake is trusting the Chrome Web Store listing as a proxy for safety. A four-star rating and a large install count tell you the extension is popular, not that its permission set is minimal or unchanged since you last checked.

The third mistake is assuming broad-sounding permissions equal the real risk and narrow ones are automatically safe. Researchers who studied malicious browser extensions across the Chrome and Firefox stores in 2025 found that attackers didn't need sweeping access to do damage — permissions as ordinary-sounding as activeTab, scripting, and storage were sufficient to execute harmful actions in both stores. That finding matters for how you audit a browser extension's permissions: it isn't about hunting for the one scary-sounding string, it's about asking what the granted permissions let the code do in combination, and how easily that combination is abused.

Permission creep compounds all three problems. A note-taking extension you approved two years ago for "read and change data on the current site" may today request account-wide host access because the vendor bolted on a sync feature. If nobody re-audits after updates, the permission surface only grows. For a fuller walkthrough of what individual permission categories mean and the everyday red flags to watch for, our Chrome extension security best practices guide is a useful companion to this one.

Method 1: The Manual, Built-In Way

Chrome, Edge, and other Chromium browsers all expose the same basic tool: chrome://extensions. It costs nothing, it's already installed, and it's where every audit should start — but it has real limits worth naming before you lean on it as your whole process.

Reading What chrome://extensions Actually Shows You

Open chrome://extensions, switch on Developer mode in the top right, and click "Details" on any extension. You'll see its permissions listed in plain language, plus a "Site access" control that restricts it to "On click," "On specific sites," or "On all sites."

That Site access toggle is your fastest manual win. An extension defaulting to "On all sites" is asking for host permissions covering every page you visit. An extension that only needs "On click" is running on the narrower activeTab model, which grants access only to the tab you're actively using, only when you invoke it, as Chrome's own developer documentation on declaring permissions explains. Pulling that toggle back from "all sites" to "on click," wherever the extension supports it, is one of the highest-leverage five-minute fixes available to anyone trying to audit a browser extension's permissions without touching a single line of code.

Reading a Manifest Directly

For a sharper picture, open the extension's Chrome Web Store entry or unpack its files and read manifest.json directly. Look at two fields: permissions (API-level access such as storage, cookies, tabs) and host_permissions (which domains it can read or modify). Chrome's official permission-warnings documentation explains how these combine to produce the install-time or runtime warning a user sees, and which permission strings trigger which warning language.

Where the Manual Method Breaks Down

Reading one manifest once is manageable. Reading the manifest of every extension across a six-person firm's browsers, every time one updates, is not. The manual method has no memory: you either build your own tracking system, or re-derive the same judgment from scratch each time. It also can't tell you what an extension's code actually does with the permissions it holds — the manifest shows what's possible, not what's happening.

Method 2: A Repeatable Audit Process With a Risk-Scoring Tool

For anyone who needs to audit a browser extension's permissions across more than a handful of extensions, or repeat the exercise on a schedule, a risk-scoring tool turns a manual read into a structured, comparable output. Duo Labs' free CRXcavator filled this role for years before being discontinued; Spin.AI has since positioned its own free browser extension risk assessment as the direct successor. A workable process looks like this:

1. Inventory every extension across every browser profile your practice uses — not just the primary one. Shared paralegal machines and personal laptops used for after-hours review both count.
2. Submit each extension's Web Store listing or ID to the risk-assessment tool and let it pull the manifest, permissions, and any known risk flags: suspicious infrastructure, broad host access, or excessive third-party trackers.
3. Read the risk score's components, not just the headline number. A "medium risk" flag from a stale privacy-policy link is a different problem than one from clipboard access stacked on broad host permissions.
4. Cross-check the vendor's update history. A sudden jump in requested permissions between versions — even from a "trusted" publisher — is the single strongest signal to watch for, and it's exactly the pattern behind the Cyberhaven compromise.
5. Set a review cadence instead of a one-time pass. Quarterly is reasonable for a small practice; monthly makes sense for a firm handling regulated or especially sensitive matters.
6. Record the decision for each extension — keep, remove, or replace — along with the reasoning, so the next audit isn't starting from zero.

Manual review, a risk-scoring tool, and enterprise policy control each solve a different slice of this problem, and most practices end up using more than one:

Approach	Best for	Effort per extension	Catches silent update creep?	Produces an audit trail?
Manual chrome://extensions review	Solo practitioners, occasional spot-checks	5–10 minutes	Only if you remember to re-check after updates	Only if you write it down yourself
Risk-scoring tool (e.g., Spin.AI)	Firms auditing 20+ extensions across a team	1–2 minutes once set up	Partially — flags newly widened permissions on rescan	Yes, typically an exportable report
Enterprise policy control (Chrome Enterprise / admin console)	IT-managed firms enforcing a standing policy	Ongoing, policy-based rather than per-check	Yes — can block installs or updates outside an allowlist	Yes — centralized admin logs

None of the three replaces the other two. Policy control stops unapproved extensions from reaching a managed browser at all, but someone still has to decide what belongs on the allowlist — which is exactly what the manual read and the risk-scoring tool are for.

A Worked Example: Auditing "RedlinePro" End to End

Say a litigation associate at a mid-size firm installs "RedlinePro," a generic contract-redlining extension that adds a toolbar button for comparing two PDF versions inline. Here's what it looks like to actually audit a browser extension's permissions on a specific, concrete case rather than in the abstract.

Its chrome://extensions Details page lists: activeTab, scripting, storage, host_permissions: <all_urls>, and cookies.

Under Method 1, most of this reads cleanly. activeTab and scripting together are normal for a tool that injects a comparison UI on demand — that's the intended Manifest V3 pattern. storage is unremarkable; most extensions cache settings locally. But host_permissions: <all_urls> paired with cookies is worth stopping on: why does a PDF comparison tool need cookie access on every domain, rather than only the document-hosting site in use?

Running it through Method 2's risk-scoring tool confirms the manual instinct and adds one more fact: the vendor shipped a permissions-widening update eight months earlier, with no changelog entry explaining why cookies was added. That's exactly the kind of silent scope creep worth treating with the same suspicion as the Cyberhaven pattern, even without proof of an actual compromise.

The decision: keep the comparison feature, since it's genuinely useful and low-risk in isolation, but replace the <all_urls> grant with a narrower access pattern if the vendor's settings support it, and email the vendor asking why cookies is requested. If there's no satisfying answer within a reasonable window, remove the extension and look for an alternative scoped to activeTab only.

That's the keep/remove/replace decision every audit should land on: keep what's justified, remove what isn't, replace what's justified in concept but overbroad in implementation.

How to Organize and Retrieve What You Just Audited

An audit you can't reproduce in six months isn't really an audit — it's a favor to your future self that you forgot to write down. For lawyers and analysts this matters doubly: if a regulator ever asks what due diligence your team did on the tools handling a matter, "we looked at it once" is a far weaker answer than a dated, retrievable record.

This is where a note-and-capture tool, not a security scanner, is the right instrument — you already have your findings from Method 2; now you need them organized and citable. WebSnips is built for that second half of the job. Its own extension follows a Manifest V3 minimal-permissions design, with no broad host access and no externally_connectable — a reasonable benchmark for what "minimal" should look like elsewhere. When you finish an audit, you can save the extension's Chrome Web Store listing and manifest excerpt as a Snip through the capture modal, which renders in a closed ShadowRoot so the page you're capturing from can't read what you're saving. Write your keep/remove/replace reasoning in a linked Note, and tag the whole record with a Label like "extension-audit-Q4."

At review time, Creator Studio can pull that quarter's audit Snips and Notes together into a single written report with citations back to each source, instead of you reconstructing the reasoning from memory or a scattered email thread.

To be clear about the boundary: WebSnips doesn't scan or score other extensions' permissions for you — that's what Method 2's risk-scoring tool is for. What WebSnips gives the finished audit is a permanent, searchable, dated home instead of a folder of loose bookmarks that quietly rot. If you want the fuller version of that capture discipline applied to research generally, our ultimate guide to web clipping covers the workflow end to end, and our personal knowledge management guide covers how to connect those findings to everything else you know.

Mistakes to Avoid

• Treating the install prompt as a one-time check. Permissions and scope can grow with routine updates, silently.
• Judging risk by permission name alone. Ordinary-sounding permissions, bundled together, can be just as dangerous as one alarming-looking one.
• Skipping the manifest and relying only on star ratings. Popularity is not a permissions audit.
• Auditing once and never re-running the process. Set a cadence, or the audit decays the moment the vendor ships an update.
• Never writing down why you kept, removed, or replaced an extension. You'll redo the same analysis from scratch next quarter.
• Assuming enterprise policy tools remove the need for judgment. They enforce a policy; someone still has to decide what that policy allows.

FAQ

How often should I audit a browser extension's permissions? Quarterly is a reasonable floor for a small practice handling confidential material; monthly is safer if the firm works with regulated data or high-value matters. Re-run the check immediately after any extension pushes a major update.

Is activeTab always safer than broad host_permissions? Not automatically. The 2025 arXiv research on malicious extensions found that activeTab, scripting, and storage alone were enough for attackers to cause harm — narrower permissions reduce your exposure, but they don't eliminate the need to check what an extension actually does with them.

Do enterprise Chrome policies replace the manual and tool-based audit steps? No. Policy control decides which extensions a managed browser can install at all, but someone still needs to review each candidate before it goes on that allowlist — that's the job the earlier two methods do.

What's the single fastest thing I can check right now? Open chrome://extensions, click "Details" on anything you don't fully recognize, and set "Site access" to "On click" instead of "On all sites" wherever the extension allows it.

Key Takeaways

• Re-check permissions after updates, not just at install — silent scope creep is the norm, not the exception.
• Use chrome://extensions → Details → Site access as your five-minute baseline check on every extension in the browser.
• Don't assume a permission is safe because its name sounds ordinary; activeTab, scripting, and storage have all been used in real attacks.
• For more than a handful of extensions, or a firm-wide review, use a risk-scoring tool rather than manual reads alone.
• Cross-check each extension's update history for sudden permission jumps — that pattern preceded the Cyberhaven supply-chain compromise.
• Land every audit on a keep, remove, or replace decision, and write the reasoning down where you can find it again.
• Treat the finished audit as a record worth archiving with dates and source links, not a one-time mental note.

Once you've made your keep/remove/replace calls, give the write-up itself a permanent home: install WebSnips and start saving your audit findings as dated, searchable Snips and Notes instead of a scattered thread of emails and browser bookmarks.