Mustafa ERBAY

Posted on Aug 10 • Originally published at mustafaerbay.com.tr

Auditing Browser Extension Permissions: Finding Data Access

#guide #software

Browser extensions often request permissions that users quickly approve during installation; however, the scope of these permissions and their data access capabilities are frequently overlooked. This situation carries significant risks for data security and privacy, as the permissions requested by a browser extension can allow it to access all of a user's online activities. In this article, we will step through the process of Auditing Browser Extension Permissions: Finding Data Access, understanding what data extensions access and why, and how to manage potential security vulnerabilities.

Understanding how much authority an extension has is the first step in protecting your digital assets. Regular audits to ensure extensions only perform their promised functions and do not access unnecessary data are an indispensable part of modern internet usage.

Why Are Browser Extension Permissions So Important?

Browser extensions are powerful tools that enrich our daily internet experience, increase productivity, and automate specific tasks. However, this power also brings serious security and privacy risks. For extensions to function correctly, they need to request access permissions to certain system resources and data, and these permissions are usually approved in bulk during the installation phase. Users often click the "Accept" button quickly, granting broad access without reading the permission lists.

The importance of this situation lies in the fact that an extension can potentially access any information and what it can do with that information. For example, an extension with "read and change all your data on the websites you visit" permission can read, save, and even send sensitive information (passwords, credit card numbers) you enter into forms, text, and images on every web page you visit to a remote server. When developing an ERP for a manufacturing company, auditing such external components is vital to minimize the risk of critical data leaking to the internet. An accidentally installed or malicious extension can lead to corporate data exfiltration or internal system access. Therefore, meticulously auditing browser extension permissions is a fundamental component of both personal and corporate security strategies.

Types of Permissions Requested by Extensions and Their Meanings

Browser extensions request various types of permissions to perform different functions. Each of these permissions determines what kind of actions the extension can perform in your browser or on the internet, and what data it can access. Correctly understanding the meaning of permissions is the first step in evaluating what an extension truly needs. For example, it might seem logical for a screenshot extension to request "read and change all your data on the websites you visit" permission, but a weather extension requesting this permission should raise suspicion.

Below are some frequently encountered permission types and what they mean:

Read and change all your data on the websites you visit: This is one of the broadest and most dangerous permissions an extension can request. It allows the extension to access, read, modify, and even capture form data (passwords, credit cards, personal information) on all web pages you visit (HTML, CSS, JavaScript). Such broad permissions are typically used via APIs like tabs, scripting, webRequest, or declarativeNetRequest.
Access your browsing history: The extension can read the URLs of sites you visit, visit times, and other historical data. This can be used to build your user profile or for ad targeting. Access to such data is usually associated with the browsingData API.
Access your downloads: The extension can access, monitor, modify, or delete files you download through your browser. Functions like downloads.setUiOptions() in Chrome might rely on this permission.
Access your tabs: The extension can list your open tabs, read their URLs, close them, open new tabs, or modify tab content. This functionality is provided by the tabs API.
Access your clipboard: The extension can access text you copy and paste. This carries the risk of sensitive information (passwords, API keys) being leaked. Permissions might be required for functions like document.execCommand('paste').
Display notifications: The extension can send system notifications. In browser extensions, this permission is used to inform the user.
Access your cookies: The extension can access cookies stored by websites you visit. Cookies can contain session information and user identities. This is managed by the cookies API.
Access data on your device: In some cases, extensions may request access to your file system. This is especially true for extensions that process local files but should be handled with caution. Generally, such access requires storage APIs or specific permissions for file operations.

⚠️ Principle of Least Privilege

The permissions requested by an extension should be proportionate to the functionality it offers. If an extension requests much broader permissions than it promises, this is a sign of a security risk. Always consider the "principle of least privilege": you should only grant a software or extension the permissions that are absolutely necessary for it to function.

Understanding these permission types allows you to make an informed decision before installing an extension. Rejecting broad permissions that do not align with the extension's purpose or seeking an alternative extension is a critical step for your digital security.

How to View Permissions of Installed Extensions

Regularly checking which permissions your browser extensions have is an important part of digital hygiene. While this auditing process varies slightly depending on the browser you use, the basic steps are generally similar. You can usually access this information by navigating to the extensions section from your browser's settings menu.

Viewing Extension Permissions in Google Chrome

Access the Extensions Page: Open your Chrome browser. Type chrome://extensions into the address bar and press Enter. Alternatively, click the three vertical dots menu in the top right corner of your browser, hover over More Tools, and select Extensions.
Go to Extension Details: On the page that opens, you will see all your installed extensions. Each extension has a Details button below or next to it. Click the Details button for the extension you want to inspect.
Review Permissions: On the extension's detail page, you will see the Permissions heading on the left or in the middle of the page. This section clearly lists what capabilities the extension has. Here, for example, you can see permissions like "Read and change all your data on the websites you visit."
Manage Permissions (Optional): For some extensions, you can directly edit or restrict permissions from this page. Especially if options like "On specific sites" or "On click" are offered, you can narrow the scope of the extension's capabilities.

Viewing Extension Permissions in Mozilla Firefox

Access the Add-ons and Themes Page: Open your Firefox browser. Type about:addons into the address bar and press Enter. Alternatively, click the three horizontal lines menu in the top right corner of the browser and select Add-ons and themes.
Go to Extension Details: On the page that opens, you will see your installed extensions. Click on the extension you want to inspect or select Manage from the three-dot menu to its right.
Review Permissions: On the extension's detail page, there is a Permissions tab on the left. Click this tab to list all permissions requested and held by the extension.
Manage Permissions (Optional): Firefox, similar to Chrome, can provide more granular control for some permissions. For example, you can set site data access permission to "Always," "On click," or "On specific sites."

Viewing Extension Permissions in Microsoft Edge

Microsoft Edge, being Chromium-based, has a similar interface to Chrome.

Access the Extensions Page: Open your Edge browser. Type edge://extensions into the address bar and press Enter. Alternatively, click the three horizontal dots menu in the top right corner of the browser, hover over Extensions, and select Manage extensions.
Go to Extension Details: Click the Details button for the extension you want to inspect.
Review Permissions: On the detail page, you will see the Permissions section. All capabilities held by the extension are listed here.
Manage Permissions (Optional): If necessary, you can change or restrict permissions here. Especially the "When you click the extension" option enhances security by allowing the extension to access site data only when you interact with it.

ℹ️ Regular Auditing is Important

It's good practice to review extension permissions periodically, for example, once a month. Extension updates might request new permissions, and you might have approved them unknowingly. Removing old and unused extensions also reduces security risks.

By following these steps, you can clearly see how much authority your browser extensions have and make informed decisions for your digital security.

Methods for Monitoring Real-time Data Access by Extensions

Knowing only which permissions browser extensions have is not enough; it's also important to understand how they actually use these permissions and what data they interact with. Especially if you suspect an extension is exhibiting suspicious behavior, the browser's built-in Developer Tools and other monitoring methods can help you observe this data access. These methods allow you to determine if extensions are making network requests in the background, manipulating the DOM, or leaving unexpected messages in the console.

Using Browser Developer Tools

Developer Tools is a powerful set for inspecting the runtime behavior of web pages and extensions.

Observe Network Activity (Network Tab):
- Open Developer Tools in your browser by pressing F12 or right-clicking and selecting Inspect.
- Switch to the Network tab.
- This tab shows all network requests (HTTP/HTTPS) made by your browser. You can monitor here if an extension is sending data to a remote server. If an extension makes requests to irrelevant or suspicious URLs for its functionality, this could be a sign of data leakage. Pay particular attention to POST requests and their content. The webRequest API is used to monitor and modify such traffic.
Examine Console Messages (Console Tab):
- The Console tab shows JavaScript errors, warnings, and console.log outputs.
- Some malicious extensions might leave traces in the console during debugging or data collection. Unexpected or cryptic console messages could indicate that the extension is doing something in the background.
Inspect Source Code (Sources Tab):
- The Sources tab shows all JavaScript files loaded by the page.
- Extensions often inject their own JavaScript files into pages. In this tab, you can look for scripts that appear suspicious or are unrelated to the page's original code. This requires a more advanced inspection but is useful for understanding an extension's DOM manipulations or data capture logic.

`about:debugging` for Firefox

For Firefox users, the about:debugging page allows for a deeper inspection of installed extensions.

Type about:debugging#/runtime/this-firefox into the address bar.
Here you will see an Inspect button for each installed extension.
Clicking the Inspect button opens a separate Developer Tools window for the extension's own background process. In this window, you can directly inspect the extension's JavaScript code, storage, and network requests. This is a very powerful tool for seeing what the extension is doing independently of the main browser window.

Network Traffic Monitoring Tools

For more advanced auditing, you can use tools that monitor network traffic at the system level:

Wireshark: A powerful network protocol analyzer that can capture all packets passing through your network interface. It can be used to see which IP addresses the extension connects to and what data it sends. However, this tool can be complex due to high data volume and requires filtering.
Local Proxy Tools (Fiddler, Burp Suite Community Edition): These tools capture all HTTP/HTTPS traffic passing through your browser, allowing you to inspect and even modify it. They are ideal for seeing all network requests made by an extension and their content in detail. They can also decrypt HTTPS traffic (but you need to install their root certificates on your system for this).

💡 Example Scenario: Detecting a Suspicious Extension

While browsing an e-commerce site, an unusual discount pop-up appeared, and you noticed your browser slowing down in the background. Opening Developer Tools and looking at the Network tab, you suddenly saw multiple POST requests made to analytics.maliciousdomain.com. The content of these requests included information such as product prices and product IDs of the items you viewed. This is a clear sign that an installed extension is collecting data and sending it to a remote server. In this case, you should check the permissions of the relevant extension and remove it immediately if necessary.

By using these methods, you can understand not only what an extension has permission to access but also how it uses those permissions in more detail. This allows you to proactively manage your data security.

Assessing Potential Risks and Restricting Permissions

After viewing the permissions requested by a browser extension, the next critical step is to assess the potential risks of these permissions and restrict any that seem unnecessary or dangerous. Since each extension has different functionality, each permission list has a different risk profile. When making this assessment, you should consider the extension's main purpose and which permissions it absolutely needs for that purpose.

Risk Assessment Steps

Functionality vs. Permission Match:
- Consider the promised function of the extension. For example, a "URL shortener" extension only needs access to the current tab's URL and should not need "read and change all your data on the websites you visit" permission.
- If a permission seems irrelevant to the extension's core function, this is a high-risk indicator.
Developer Reliability:
- Research the extension's developer. Avoid extensions from unknown or suspicious-looking developers.
- The extension's popularity, reviews, and last update date can also provide clues about reliability. Extensions with many negative reviews or those not updated for a long time can be risky.
Data Sensitivity:
- Consider how sensitive the data is that the extension is requesting access to. Permissions like browsing history, cookies, and clipboard access can put your personal and financial information at risk.
- Especially when working on corporate networks, an extension's access to corporate data poses a significant risk.

Restricting and Managing Permissions

Modern browsers offer users the ability to manage extension permissions after installation. This allows you to reduce risks by narrowing an extension's capabilities rather than completely removing it.

Restricting Host Permissions:
- In most browsers, you can restrict an extension's "read and change all your data on the websites you visit" permission to work only on specific sites or "when clicked."
- Chrome/Edge: On the extension details page, find the "This can read and change site data" section. Here you can choose from "On all sites," "On specific sites," or "When you click it." The "When you click it" option ensures the extension is active only when you click its icon, which is one of the safest approaches.
- Firefox: You can find similar options in the "Permissions" tab on the extension details page. Under "Runtime host permissions," you can manage which sites the extension will work on and how it will operate.
Rejecting Unnecessary Permissions:
- Some permissions may be entirely unnecessary for the extension's function. For example, it's illogical for a "theme changer" extension to access your location. In such cases, if the browser offers the option to disable permissions individually, turn them off.
Disabling/Removing Unused Extensions:
- Completely disable or remove extensions you haven't used for a long time or no longer need. The fewer extensions installed, the smaller the potential risk area.

This flow summarizes the extension management process. Restricting permissions, while not a complete solution, can significantly reduce the potential harm of an extension. Adopting an active and conscious approach to securing your digital assets is essential.

Additional Tools and Approaches for Advanced Auditing

While simple permission checks and developer tools are sufficient for most situations, more advanced tools and approaches may be needed, especially in high-security environments or when you want to investigate suspicious behavior more deeply. These methods allow you to analyze not only the permissions of browser extensions but also their runtime behavior, file system interactions, and network traces in more detail.

Additional Extension Management Tools in the Browser

Some browsers or third-party developers offer additional extensions to manage extensions. Such "extension manager" extensions allow you to list installed extensions in bulk, enable and disable them with a single click, and in some cases, even manage their permissions more granularly. This can simplify the auditing process, especially for people who use many extensions. However, when using an extension manager extension, remember that this extension itself will need broad permissions; therefore, ensure it comes from a trusted source.

Operating System Level Monitoring

For more advanced auditing, you can monitor the effects of extensions on the operating system:

File Integrity Monitoring (FIM): Tools like auditd or system monitoring solutions like osquery can be used to monitor whether extensions are creating unexpected files or modifying existing ones in browser profile folders or other system directories. If an extension is malicious, it might try to write its harmful code or data collection logs to such locations.
Process Monitoring: Browsers often launch separate processes for each tab and extension. With tools like htop (Linux), Process Explorer (Windows), or Activity Monitor (macOS), you can observe if browser processes are consuming more CPU or memory than expected. Abnormal resource consumption can be a sign that an extension is performing intensive background operations or carrying out malicious activity.

Network and Traffic Analysis

We previously mentioned the Developer Tools' network tab, but specialized tools are available for more in-depth analysis:

Local Proxy and Traffic Inspection: Tools like mitmproxy or OWASP ZAP can capture all HTTP/HTTPS traffic and inspect its content. These tools allow you to decrypt the content of encrypted requests made by extensions (after root certificate installation). This way, you can see exactly what data the extension is sending to which servers.
Monitoring DNS Queries: Extensions can make DNS queries to new domains to send data. Examining logs on a local DNS server (e.g., Pi-hole) can reveal suspicious domains that extensions are communicating with.

🔥 Risks and Usage of Advanced Tools

Using advanced tools like Wireshark or local proxy tools requires network and system knowledge. Misconfiguration can jeopardize your system security or interrupt your internet access. Before using these tools, ensure you understand how they work and their potential effects. Especially in corporate environments, you may need to comply with IT security policies for the use of such tools.

These advanced auditing methods provide valuable insights, especially when targeted attacks or sophisticated malware are suspected. However, for the average user, regular permission auditing and basic use of browser developer tools are usually sufficient. The important thing is to make your security posture proactive and continuous.

Best Practices for Extension Security and Common Vulnerabilities

Ensuring browser extension security doesn't end with just auditing permissions; it also requires adopting general security practices and being vigilant against common types of vulnerabilities. As malicious actors constantly develop new methods, we must also keep our defense mechanisms up-to-date.

Common Extension Security Vulnerabilities

Malicious Extensions: The most obvious risk is extensions that contain outright malware. These extensions are designed to steal data, inject ads, mine cryptocurrency, or conduct phishing attacks. They often disguise themselves with seemingly legitimate functionality.
Supply Chain Attacks: Occur when a trusted extension developer's accounts are compromised, and malicious code is injected into the extension and updated. Users may unknowingly install malware when updating an extension they trust.
Vulnerable Extensions: An extension's own code may contain security flaws (e.g., XSS, logic errors similar to SQL Injection). These vulnerabilities allow malicious websites or other extensions to perform unauthorized actions or access data in the browser by exploiting the vulnerable extension.
Excessive Permission Usage: The extension requests much broader permissions than necessary for its functionality. As mentioned earlier, this increases the potential for misuse.
Data Leakage: The extension sends collected data to remote servers through insecure means (e.g., unencrypted HTTP) or accidentally makes data publicly accessible.

Best Practices for Extension Security

Install Only from Trusted Sources: Always download extensions from official browser stores (Chrome Web Store, Firefox Add-ons, Edge Add-ons). Avoid extensions offered through third-party websites or pop-ups.
Check Developer and Reviews: Before installing an extension, research the developer's reputation, user reviews, and how long the extension has been active. Be suspicious of very new, low-download, or poorly reviewed extensions.
Carefully Review Permissions: Never skip the permissions requested when installing an extension. For permissions you don't understand or that seem irrelevant to the functionality, research alternatives to the extension.
Apply the Principle of Least Privilege: Grant extensions only the minimum necessary permissions to function. Use your browser's permission management features to enforce these restrictions.
Remove or Disable Unused Extensions: The fewer active extensions, the smaller the attack surface. Regularly review your extension list and clean up those you don't need.
Keep Your Browser and Extensions Updated: Developers release updates to fix security vulnerabilities in extensions. Enable automatic updates for your browser and all extensions. This is one of the simplest ways to protect against known vulnerabilities.
Use Antivirus and Security Software: Quality antivirus software can prevent malicious extensions from infiltrating your system or performing harmful actions.
Awareness and Skepticism: Always be vigilant when browsing the internet. Unexpected pop-ups, advertisements, or deviations from your browser's normal behavior could be a sign of a malicious extension.

By following these best practices and being aware of potential vulnerabilities, you can maximize your digital security and privacy while benefiting from the convenience offered by browser extensions.

Conclusion

Browser extensions are indispensable tools that enrich our internet experience; however, the security and privacy risks they pose should not be overlooked, as much as the convenience they offer. The process of Auditing Browser Extension Permissions: Finding Data Access that we discussed in this article is a critical digital hygiene practice that every internet user should adopt. Understanding the scope of permissions requested by extensions, evaluating how well these permissions align with their functionality, and restricting these capabilities when necessary forms the foundation of protecting our personal and corporate data.

Remember, security is an ongoing process. Consciously evaluating every extension you install, regularly auditing its permissions, monitoring for suspicious behavior, and cleaning up old or unused extensions are key to keeping your digital footprint secure. By taking these steps, you can fully leverage the benefits offered by extensions, minimize potential risks, and ensure a safer online experience.