Browser Extension Permission Audits: How to Protect Sensitive Business Websites

• **The Risk:** Browser extensions can read, modify, and exfiltrate data across enterprise web portals, identity providers, and SaaS dashboards if granted broad host permissions and relevant API privileges.
• **The Reality:** Approving an extension for installation is distinct from granting it unrestricted runtime access to sensitive corporate websites.
• **The Fix:** Implement browser policy engines to block installation by default, enforce `runtime_blocked_hosts` on sensitive domains across Chrome and Edge, apply Firefox `restricted_domains` inside the default `ExtensionSettings` policy, and audit extension manifests periodically.

A finance administrator logs into an enterprise payroll portal, opens an internal analytics sheet, and reviews quarterly compensation files. Unbeknownst to the security team, a popular document-utilities browser extension installed six months prior holds host permissions to read and modify data on all web pages. When the developer of that extension updates its content scripts or modifies functionality on pages where host access is already granted, the extension executes updated logic inside the admin's active browser session.

Browser extensions are part of the workforce endpoint security surface. Organizations invest heavily in cloud IAM, network firewalls, and endpoint protection agents, yet workforce browser instances often run third-party extensions capable of inspecting DOM elements inside authenticated business portals.

Protecting sensitive business websites requires a structured permission-audit framework that separates extension installation approval from runtime website access.

1. What Browser Extension Permissions Actually Allow

Browser extensions operate inside the browser rendering context with privileges that standard web pages do not possess. To evaluate risk accurately, security teams must distinguish between specific permission categories:

• Host Permissions (Site Access): Define matching origins where relevant extension APIs receive additional privileges. Host permissions enable programmatic script injection, receiving webRequest events, performing cross-origin extension fetches, and accessing cookies when the cookies API permission is also granted.
• Content Scripts: JavaScript files injected directly into specified web pages. When host permissions permit execution, content scripts execute in the context of the page DOM, enabling them to inspect input fields, capture keystrokes, or modify displayed text.
• Cookies API Permission: Access through the cookies API requires the explicit cookies API permission together with matching host permissions for the targeted domain. Host permissions alone do not grant access to the chrome.cookies or browser.cookies API.
• DeclarativeNetRequest & Web Request APIs: Provide rule-based request handling. Under Manifest V3 declarativeNetRequest, block and upgradeScheme actions can operate without host permissions, whereas redirect and modifyHeaders actions require applicable host permissions.
• Native Messaging: Allows an extension to exchange messages with a separately installed native application outside the browser process, requiring specific endpoint validation for the target native binary.

Broad permissions do not automatically indicate malicious intent; many legitimate utility, accessibility, and developer tools require extensive DOM access to function. However, broad host permissions combined with API access create high-value targets for supply-chain compromise, session hijacking, and unauthorized data collection.

2. Start With an Accurate Extension Inventory

Security leads cannot restrict extension risks without a complete, up-to-date inventory of every extension active across workforce browsers. Self-reporting and manual spot-checks can miss extensions installed across distributed browser profiles.

Enterprise management platforms provide centralized inventory visibility:

• Google Chrome Enterprise Core: Reports installed extension IDs, extension names, requested permissions, store update channels, and version numbers across managed Chrome profiles via the Google Admin Console.
• Microsoft Edge Management Service: Displays browser add-on telemetry, installation sources, and management options for Microsoft Entra ID managed enterprise endpoints.
• Mozilla Firefox Enterprise Policies: Configures add-on policies via policies.json or enterprise policy templates. While Firefox Enterprise Policies enforce configuration and installation constraints, organizations managing Firefox typically pair policy enforcement with endpoint management (MDM/EDR) or browser log collection for centralized inventory tracking.

When local profile inspection is required for unmanaged or troubleshooting scenarios, administrators should avoid relying on hard-coded directory assumptions. Instead, instruct users or administrative scripts to open the browser diagnostic page (chrome://version, edge://version, or about:support in Firefox) to locate the exact active profile path before inspecting local storage structures.

An actionable inventory must record the extension ID, publisher name, requested permissions, store update channel, installation type (user-installed vs. force-installed), and assigned business owner.

3. Identify Sensitive Websites Before Reviewing Extensions

Not all web pages carry equal risk. Auditing every URL requested by every extension produces operational noise. Instead, classify corporate web surfaces into high-value security tiers:

1. Identity & Access Management: IdP admin consoles, SSO portals, MFA configuration pages, and password manager dashboards (e.g., Okta, Microsoft Entra ID, Ping Identity).
2. Source Code & Infrastructure: Version control repositories, CI/CD pipelines, cloud management consoles, and DNS management panels (e.g., GitHub, GitLab, AWS Console, Cloudflare).
3. Finance & Operations: Payroll platforms, corporate banking portals, ERP systems, and billing dashboards (e.g., Stripe, NetSuite, Workday).
4. Customer Data Platforms: CRMs, customer support queues, and primary database consoles (e.g., Salesforce, Zendesk, HubSpot).

Security Policy Rule: No third-party browser extension—regardless of productivity utility—should possess unrestricted host permissions or content script execution on Tier-1 Identity, Infrastructure, or Financial portals unless an explicit enterprise exception is documented and approved.

4. Separate Installation Approval From Website Access

A fundamental flaw in traditional extension management is treating extension approval as a binary decision: either an extension is allowed, or it is blocked.

Modern enterprise browser policies allow administrators to approve an extension for general productivity while restricting its runtime execution on sensitive corporate domains. An employee may use an approved document converter or translation utility on public reference sites, but that same extension should be programmatically blocked from reading DOM elements on corporate financial or identity dashboards.

By decoupling installation permission from runtime host access, IT teams can support workforce productivity without exposing sensitive portals to unnecessary supply-chain risk.

5. Review Host Permissions, Content Scripts and Native Messaging

When evaluating an extension for enterprise allowlisting, security reviewers must inspect three critical manifest elements:

+-------------------------------------------------------------------+
|               Extension Manifest Security Audit                   |
+-------------------------------------------------------------------+
| 1. Host Permissions   --> Does it require <all_urls> or specific? |
| 2. Content Scripts    --> Which domains receive injected JS?      |
| 3. Native Messaging   --> Does it call local OS executable binary?|
+-------------------------------------------------------------------+

1. Host Permission Scope: Examine whether the extension requests broad wildcards like *://*/* or limits access to explicit domains. Prefer extensions that utilize optional permissions, requesting site access only when invoked by the user.
2. Content Script Matches: Verify which domains trigger automatic script injection. Content scripts executing on login or checkout pages present elevated risk.
3. Native Messaging Declarations: Confirm whether nativeMessaging is declared. Extensions communicating with local desktop applications require separate endpoint security validation for the target binary.

6. Apply Chrome, Edge and Firefox Controls Carefully

Enterprise policy syntax varies across browser vendors. Security teams must implement platform-specific policy rules accurately.

Google Chrome Enterprise Controls

Chrome uses the ExtensionSettings policy key. Crucially, per-extension settings in Chrome do not automatically inherit wildcard runtime_blocked_hosts from the "*" default configuration. When configuring a specific extension ID, administrators must explicitly declare runtime_blocked_hosts on that extension's configuration object to maintain domain restrictions:

{
  "ExtensionSettings": {
    "*": {
      "installation_mode": "blocked",
      "runtime_blocked_hosts": [
        "*://*.okta.com",
        "*://*.github.com",
        "*://console.aws.amazon.com",
        "*://*.stripe.com"
      ]
    },
    "nngmjgfppbploalmjianfhjhalhhgocl": {
      "installation_mode": "allowed",
      "runtime_blocked_hosts": [
        "*://*.okta.com",
        "*://*.github.com",
        "*://console.aws.amazon.com",
        "*://*.stripe.com"
      ],
      "runtime_allowed_hosts": [
        "https://*.google.com"
      ]
    }
  }
}

Microsoft Edge Enterprise Controls

Microsoft Edge supports ExtensionSettings with identical JSON structure for runtime_blocked_hosts and runtime_allowed_hosts. Administrators should clearly distinguish installation controls (ExtensionInstallBlocklist, ExtensionInstallAllowlist) from runtime host access controls (ExtensionSettings with runtime_blocked_hosts / runtime_allowed_hosts or blocked_permissions where documented).

Mozilla Firefox Enterprise Policy

Firefox configures extension controls via ExtensionSettings inside policies.json. Firefox ExtensionSettings supports valid documented installation_mode values including "blocked", "allowed", "force_installed", and "normal_installed". Mozilla documents restricted_domains as a setting usable within the default "*" configuration under ExtensionSettings to restrict content script execution on specified domains:

{
  "policies": {
    "ExtensionSettings": {
      "*": {
        "installation_mode": "blocked",
        "restricted_domains": [
          "okta.com",
          "github.com",
          "console.aws.amazon.com",
          "stripe.com"
        ]
      },
      "[email protected]": {
        "installation_mode": "allowed"
      }
    }
  }
}

Note: Mozilla documents restricted_domains inside the default "*" ExtensionSettings object as specific domains where content scripts are restricted from running across extensions.

7. Create a Repeatable Permission-Audit Matrix

Establish an operational matrix to track approved extension exceptions, host permission scopes, and review lifecycles:

8. Recheck Permissions After Updates

Browser extensions update automatically via vendor web stores. The security impact of updates depends on browser platform configurations and installation types:

• Chrome User-Installed Extensions: In Google Chrome, when a user-installed extension modifies its manifest to request significant new permissions, Chrome disables the extension until the user accepts the updated permission prompt.
• Managed-Extension Updates: Managed-extension update behavior depends on enterprise policy and deployment configuration; administrators should review updated permissions through their management tooling.
• Code Logic Updates: Developers can update content script logic or backend API endpoints without changing manifest permission strings. An update that changes code without adding a new warning-triggering permission may not generate a new permission prompt.

Establish a quarterly audit cycle to inspect active extension manifests against your baseline inventory, ensuring that background updates have not introduced scope creep.

9. A Minimum Browser Extension Governance Policy

Implement this concise 5-point policy checklist to establish robust extension governance:

1. Default Block Installation: Configure installation_mode: "blocked" as the global default in ExtensionSettings across Chrome, Edge, and Firefox.
2. Curate an Enterprise Allowlist: Allow only vetted extension IDs required for specific, documented business functions.
3. Enforce Domain Blocklists Explicitly: Apply runtime_blocked_hosts (including explicit declarations within per-extension policy objects) in Chrome/Edge, and restricted_domains within default ExtensionSettings in Firefox.
4. Assign Business Owners & Expiration: Require every extension exception to specify an internal business owner and an expiration date.
5. Include Extensions in Incident Response: Incorporate extension permission reviews into security incident investigation playbooks alongside testing emergency admin access, reviewing browser profile isolation, and auditing software vendor security evidence.

10. Sources and Further Reading

1. Google Chrome Enterprise Policy Reference: Chrome ExtensionSettings Policy Documentation
2. Google Workspace Admin Help: Set up Chrome Apps and Extensions Usage Report
3. Microsoft Learn: Microsoft Edge Enterprise Policy Reference: ExtensionSettings
4. Mozilla Firefox Administrator Reference: Firefox ExtensionSettings Policy Reference
5. MDN Web Docs: WebExtensions Host Permissions Specification
6. MDN Web Docs: WebExtensions Cookies API Reference
7. MDN Web Docs: WebExtensions Content Scripts Documentation
8. MDN Web Docs: WebExtensions Native Messaging Specification
9. MDN Web Docs: WebExtensions declarativeNetRequest API Reference
10. Chrome Developer Documentation: Extension Permission Warnings & Updates