Browser Extension Security Analysis

Browser extensions enhance functionality but can also introduce security risks. A thorough security analysis involves assessing permissions, code integrity, data handling, and potential attack vectors. Below is a structured approach to browser extension security analysis.

1. How to Audit Browser Extensions

Auditing a browser extension involves a systematic review of its code, permissions, and behavior to identify potential security flaws. Below is a step-by-step guide to auditing browser extensions:

1.1. Static Code Analysis

• Objective: Review the extension’s source code without executing it.
• Steps:Access the Code: Extract the extension’s source code (usually in JavaScript, HTML, and CSS).Review Permissions: Check the manifest.json file for requested permissions. Ensure that the permissions are minimal and necessary for the extension’s functionality.Analyze JavaScript: Look for insecure coding practices, such as:Use of eval() or innerHTML.Insecure use of APIs (e.g., XMLHttpRequest, fetch).Hardcoded secrets or credentials.Check for Third-Party Libraries: Identify any third-party libraries used and ensure they are up-to-date and free from known vulnerabilities.Content Security Policy (CSP): Verify that the extension has a strong CSP to mitigate cross-site scripting (XSS) attacks.

Tools: https://crxaminer.tech/, ExtAnalysis and https://robwu.nl/crxviewer/, Extension Auditor Chrome Extension

Take an example of Wappalyzer as extension to audit now open chrome url of wappalyzer https://chromewebstore.google.com/detail/wappalyzer-technology-pro/gppongmhjkpfnbhagpmjfkannfbllamg?hl=en.

gppongmhjkpfnbhagpmjfkannfbllamg is known as extension id

If you are using https://crxaminer.tech/. you simply need to input the extension in the input field as shown in below

Click on analyze you can see the Security Analysis , Details and Manifest file

What is importance of manifest file in browser extension?

The manifest file (manifest.json) is a critical component of any browser extension, serving as the blueprint that defines the extension's behavior, permissions, and metadata. It is the only file that every browser extension must contain, regardless of the browser (Chrome, Firefox, Edge, etc.)

Here’s a detailed analysis of its importance:

1. Metadata Definition

The manifest file contains essential metadata about the extension, such as:

• Name: The name of the extension.
• Version: The version number of the extension, which is crucial for updates and compatibility.
• Description: A brief description of the extension’s purpose.
• Author: Information about the developer or organization behind the extension.

This metadata helps users and the browser understand what the extension does and who created it

2. Permissions Declaration

The manifest file specifies the permissions the extension requires to function. These permissions define what browser APIs and user data the extension can access. For example:

• Access to browser tabs (tabs).
• Access to cookies (cookies).
• Access to the user’s browsing history (history).
• Ability to intercept and modify network requests (webRequest).

By declaring permissions in the manifest, users are informed about the level of access the extension requires, and the browser can enforce security policies to prevent misuse.

3. Defining Extension Components

The manifest file outlines the various components of the extension, such as:

• Background Scripts: Persistent scripts that run in the background and handle events.
• Content Scripts: Scripts that run in the context of web pages, allowing the extension to interact with the DOM.
• Browser Action/Popup: Defines the UI elements, such as the extension’s icon and popup window.
• Options Page: Specifies the page where users can configure the extension’s settings.

These components are essential for the extension’s functionality and are defined in the manifest file

4. Content Security Policy (CSP)

The manifest file can include a Content Security Policy (CSP), which helps mitigate risks like Cross-Site Scripting (XSS) by restricting the sources from which the extension can load scripts, styles, and other resources. A strong CSP is crucial for preventing malicious code execution within the extension.

5. Resource Accessibility

The manifest file defines which resources (e.g., images, scripts, styles) are web-accessible, meaning they can be accessed by web pages or other extensions. This is important for ensuring that only authorized resources are exposed to external entities, reducing the risk of data leakage or unauthorized access

6. Compatibility and Versioning

The manifest file can specify the minimum browser version required for the extension to function properly. This ensures that the extension is only installed on compatible browsers, preventing potential issues caused by unsupported APIs or features.

7. Update and Maintenance

The manifest file plays a role in the extension’s update mechanism. When an extension is updated, the browser checks the manifest file for changes in version number, permissions, or other critical details. This ensures that users are always running the latest, most secure version of the extension.

8. Cross-Browser Compatibility

While the manifest file is primarily associated with Chrome extensions, it is also used in other browsers like Firefox and Edge, making it a standardized format for defining extensions across different platforms. This allows developers to create extensions that can be easily ported between browsers with minimal changes.

9. Security and Trust

The manifest file is a key part of the security review process when an extension is submitted to a browser’s extension store (e.g., Chrome Web Store). Reviewers examine the manifest to ensure that the extension does not request excessive permissions or include malicious code. This helps build trust between users and developers

10. Future-Proofing with Manifest V3

With the introduction of Manifest V3, Google has made significant changes to how extensions are built, focusing on improving security and performance. For example, Manifest V3 replaces background pages with service workers, which are more efficient and secure. The manifest file is central to these changes, as it defines how the extension will operate under the new architecture

Conclusion

The manifest file (manifest.json) is the cornerstone of any browser extension, defining its metadata, permissions, components, and security policies. It ensures that the extension functions correctly, adheres to security best practices, and provides users with transparency about its behavior. Without a properly configured manifest file, an extension cannot be installed or run in a browser, making it an indispensable part of the extension development process

Reverse engineer the browser extension to see the mainfesft file use the website https://robwu.nl/crxviewer/

Now place the extension url in the field as shown in below click on the open in this viewer button

Now you can see the extension is made up of js,css,html and manifest.json file .

Threat Model for Browser Extensions

Understanding how an extension interacts with the browser and external resources helps in defining the threat model. Consider the following aspects:

• Permissions and Privileges: Extensions may request broad access to web pages, browsing history, cookies, or even system files.
• Communication Channels: Data exchange between the extension, web pages, and external APIs must be controlled to prevent data leaks.
• User Authentication: Some extensions interact with authenticated sessions, making them potential targets for session hijacking.
• Malicious Code Injection: Vulnerabilities in extensions can allow attackers to execute arbitrary JavaScript, enabling phishing attacks or credential theft.
• Data Storage and Handling: Extensions may store sensitive information locally or transmit it to remote servers.

A comprehensive security assessment should cover the following areas:

A. Code Review & Integrity

• Manifest File Analysis: Check requested permissions in manifest.json. Avoid activeTab, all_urls, and host_permissions unless necessary.
• JavaScript Execution: Detect the use of eval(), setTimeout(), or setInterval() with string arguments, which can be exploited for code injection.
• External Scripts: Extensions loading JavaScript from external sources pose a security risk. Always prefer inline scripts with Content Security Policy (CSP).

B. Permissions & API Usage

• Restrict Permissions: Follow the principle of least privilege. Common high-risk permissions include:webRequest: Can intercept and modify network traffic.storage: Can store and retrieve sensitive user data.tabs: Can access user browsing history and open/close tabs.nativeMessaging: Can execute native applications on the host system.
• Evaluate Permissions: Review the permissions and optional_permissions fields in manifest.json.
• Principle of Least Privilege: Confirm that the extension only requests permissions that are absolutely necessary for its functionality.
• Sensitive Permissions: Pay special attention to permissions like:
• tabs: Access to all browser tabs.
• history: Access to browsing history.
• cookies: Access to cookies.
• webRequest: Ability to intercept and modify network requests.
• Review API Calls: Ensure secure handling of network requests (e.g., fetch(), XMLHttpRequest).

C. Data Security & Privacy

• Storage Protection: Avoid storing sensitive data in local storage. Use secure storage APIs like chrome.storage with encryption.
• Data Transmission: Ensure HTTPS for all network requests and prevent MITM attacks.
• Third-Party Tracking: Check for analytics libraries or trackers that might compromise user privacy.

D. Secure Communication

• Message Passing Security: Use chrome.runtime.sendMessage and chrome.runtime.onMessage securely.
• Validate Messages: Implement strict validation when receiving messages from content scripts or web pages to prevent DOM-based attacks.

E. Content Security Policy (CSP)

• Restrict Inline Scripts: Use strict CSP to prevent script injection.
• Avoid Wildcard Rules: script-src 'self' 'unsafe-eval' should be avoided.

F.Behavior Analysis

• Objective: Understand how the extension behaves in different scenarios.
• Steps:Test Edge Cases: Simulate unusual user interactions or inputs to see how the extension behaves.Check for Data Leakage: Ensure that the extension does not inadvertently expose sensitive data.Review Update Mechanism: Verify that the extension updates securely and does not download or execute untrusted code.

G. Third-Party Integration Review

• Objective: Ensure that third-party integrations are secure.
• Steps:Review External APIs: Check how the extension interacts with external APIs and ensure that data is transmitted securely (e.g., using HTTPS).Third-Party Scripts: Identify any third-party scripts loaded by the extension and verify their integrity.

Common Vulnerabilities in Browser Extensions

• Browser extensions are susceptible to various security vulnerabilities. Below are some of the most common ones:
• 1. Cross-Site Scripting (XSS)
• Description: XSS occurs when an extension injects untrusted data into the DOM without proper sanitization, allowing attackers to execute malicious scripts in the context of the extension or the web page.
• Example: document.getElementById("output").innerHTML = userInput;
• Mitigation:Use secure methods like textContent instead of innerHTML.Implement a strong Content Security Policy (CSP).

.2. Excessive Permissions

• Description: Extensions that request more permissions than necessary can pose a significant risk if compromised.
• Example: An extension that requests access to all tabs ("tabs") but only needs to interact with the active tab.
• Mitigation:Follow the principle of least privilege.Use optional permissions where possible.

3. Insecure Data Storage

• Description: Extensions may store sensitive data (e.g., credentials, tokens) insecurely, making it accessible to attackers.
• Example:chrome.storage.local.set({ "apiKey": "secretKey123" });
• Mitigation:Use secure storage mechanisms like chrome.storage.sync with encryption.Avoid storing sensitive data in local storage.

.4. Man-in-the-Middle (MITM) Attacks

• Description: Extensions that communicate with external servers over HTTP (instead of HTTPS) are vulnerable to MITM attacks.
• Example: fetch("https://example.com/api/data")
• Mitigation:Always use HTTPS for communication with external servers.Implement certificate pinning where applicable.

.5. Insecure Content Scripts

• Description: Content scripts that run in the context of web pages can be exploited if they interact with untrusted content.
• Example: chrome.tabs.executeScript(tabId, { code: "document.body.innerHTML = 'Hello World';" });
• Mitigation:Isolate content scripts from the web page using techniques like iframe sandboxing.Validate and sanitize all inputs.

6. Background Page Vulnerabilities

• Description: Background pages, which run persistently in the background, can be exploited if they contain vulnerabilities.
• Example: chrome.runtime.onMessage.addListener((request, sender, sendResponse) => { eval(request.code); });
• Mitigation:Avoid using dangerous functions like eval().Keep background pages minimal and secure.

7. Clickjacking

• Description: Extensions that modify the UI of web pages can be vulnerable to clickjacking, where an attacker tricks the user into clicking on something they did not intend to.
• Example: An extension that overlays a button on a web page could be exploited to perform unintended actions.
• Mitigation:Use secure UI practices and avoid overlaying elements on untrusted pages.Implement frame-busting techniques to prevent UI redressing.

8. Insecure Updates

• Description: Extensions that update their code from untrusted sources can introduce vulnerabilities.
• Example: An extension that downloads and executes code from an external server without proper validation.
• Mitigation:Use secure update mechanisms provided by the browser (e.g., Chrome Web Store).Verify the integrity of downloaded code using cryptographic signatures.

Also please refer the Google Extension Whitepaper https://docs.google.com/document/d/1pT0ZSbGdrbGvuCsVD2jjxrw-GVz-80rMS2dgkkquhTY/edit?tab=t.0

The tool ExtAnalysis has to be installed on linux platfrom

Refer the link for ExtAnalysis tool https://null-byte.wonderhowto.com/how-to/analyze-web-browser-extensions-for-possible-malware-other-malicious-activity-0236335/

Also Refer more information about vulnerabilities on extension in browser below are the links

https://palant.info/about/

https://book.hacktricks.wiki/en/pentesting-web/browser-extension-pentesting-methodology/browext-xss-example.html

Link for the tool : https://github.com/gayatriracha/ExtensionAuditor

Play with it and let me know :)