Learn to Identify and Avoid Malicious Browser Extensions

Browser extensions have become essential parts of how we browse, bank, work, and shop online. From password managers to ad blockers, these tools can significantly improve your digital life when chosen wisely. Chief among these are browser plug-ins, which extend its functionality. Almost all popular browsers support these extensions, unfortunately, making them one of the most commonly used malware attack vectors.

In this guide, you will learn about the advantages and security risks of browser extensions, the role that permissions play in ensuring your privacy when using these extensions, and some best practices when using them.

Browser extensions and their malicious counterparts

Browser extensions are small software programs that enhance your web browser by adding new functionality or modifying existing ones. Think of them as helpful extra tools that can block ads, manage passwords, check prices while shopping, or customize how websites look and behave. Legitimate extensions make your browsing experience more efficient and enjoyable.

Cybercriminals, however, have taken advantage of their popularity by creating malicious versions disguised as useful tools that secretly operate with harmful intentions. Some of these malicious browser extensions access and modify web pages, monitor your browsing activity, and interact with websites on your behalf.

While legitimate extensions request only the minimum permissions necessary for their stated purpose, malicious extensions often request more permissions than they need to access your browsing data and history.

Core tactics of malicious browser extensions

Malicious browser extensions typically operate through specific methods that can significantly impact your daily online activities, from casual browsing to important financial transactions, including:

• Permission abuse occurs when an extension requests far more access than it needs to operate. For example, a weather extension that claims to show local forecasts might request permission to track the websites you visit, allowing it to monitor everything you do online and capture sensitive information such as passwords and credit card numbers without your knowledge.
• Ad injection is where malicious extensions insert unwanted advertisements into web pages you’re viewing, appearing as pop-ups, banner ads, or even replacing legitimate advertisements with malicious ones. These injected ads disrupt your browsing experience, can lead to scam websites, or attempt to trick you into downloading additional malware.
• Data theft is one of the most serious threats posed by malicious extensions. These programs can silently capture everything you type, including usernames, passwords, credit card information, and personal details, exposing your personal information to cybercriminals. When you log into your online banking or online shopping account, the malicious extension might record your login credentials and account information.
• Traffic redirection involves redirecting your legitimate web traffic to scam websites designed to steal your information or trick you into making fraudulent purchases. This is particularly dangerous when you’re trying to access your bank’s website or other financial services, but are redirected to a convincing fake site that could capture your login credentials.
• Drive-by downloads can be triggered by these ill-intentioned browser extensions when you visit specific websites, click on seemingly innocent links or files, or even during routine browsing activities. The links and files are disguised as legitimate software updates, media files, or useful applications that, in fact, could infect your device with ransomware, keyloggers, or other types of malware.
• Cryptocurrency mining extensions secretly use your computer’s processing power to mine cryptocurrency for the extension creator, running resource-intensive calculations in the background without your knowledge or consent. This unauthorized mining activity causes your device to run more slowly, drain your laptop battery faster, consume more electricity, generate excess heat, and potentially shorten your hardware’s lifespan.

The impact of malicious browser extensions

If not caught, malicious extensions can disrupt your daily life and compromise your personal security.

Malicious extensions violate your privacy when they monitor your online behavior and track the websites you view, build a profile of your habits and preferences, and even obtain your home address and other personal details. These details can be used for identity theft, social engineering attacks, or sold to data brokers, ultimately compromising your privacy and potentially affecting your real-world safety and financial security.

When it comes to online shopping, some malicious extensions could pressure you into hasty purchase decisions, intercept your checkout process, and capture your payment information. Once cybercriminals have your shopping account credentials, they can impersonate you to make unauthorized purchases.

Similar incidents could happen with your banking and financial accounts. Malicious browser extensions can steal your login credentials, account numbers, transaction details, and eventually your money. Some cybercriminals have gone as far as opening new accounts and applying for loans using your stolen information.

The most insidious aspect of malicious browser extensions is their ability to operate silently in the background while maintaining the appearance of legitimate functionality. A malicious extension might continue providing its advertised service—such as weather updates or price comparisons—while simultaneously conducting harmful activities, making them effective at avoiding detection.

On top of the higher electricity bills, degraded device performance and browsing experience, and wasted network bandwidth, malicious extensions violate your values by turning your device into an unwitting money-making tool for cybercriminals while you bear the operational costs. Furthermore, malicious extensions could potentially expose you to additional malware or scams, and involve you in fraudulent advertising schemes.

Their impact extends beyond your own device and could affect your entire household. On the shared networks and devices, malicious extensions can spread and compromise other users.

Guidelines to stay safe with browser extensions

Chrome extensions can absolutely be safe to use when you approach them with the right knowledge and precautions. The vast majority of extensions on the official Chrome Web Store undergo Google’s review process and are built by legitimate, reputable developers who aim to enhance your browsing experience and follow security best practices.

Additionally, the Chrome Web Store’s rating system and user reviews provide valuable insights into an extension’s reliability and performance. When you stick to well-established extensions with thousands of positive reviews and regular updates, you’re generally in safe territory.

However, the extension ecosystem does present a few security challenges. The primary risks come from two main areas: permission abuse and post-installation behavior changes. When you install an extension, you give it permission to access various aspects of your browsing data and your device. Some extensions may request more permissions than they actually need, creating potential privacy and security vulnerabilities. Even more concerning, some extensions start with benign functionality but later receive updates that introduce malicious features or get sold to malicious actors who update them with data-harvesting capabilities, turning a once-safe extension into a potential threat.

To help you navigate these challenges safely, here’s a practical risk assessment framework you can use before installing any Chrome extension. This systematic approach takes just a few minutes but can save you from potential headaches down the road.

Step 1: Evaluate the source’s reputation

Start by examining who created the extension. Look for extensions developed by well-known companies or developers with established track records. Check the developer’s website and other extensions they’ve created. Extensions from companies like Google, Microsoft, or other recognized tech firms generally carry lower risk profiles. For individual developers, look for those who maintain a professional online presence and have created multiple successful extensions.

Step 2: Analyze user reviews and ratings

Don’t just glance at the overall star rating. Read the actual reviews, look for patterns in user feedback, and pay special attention to recent comments that might indicate changes in the extension’s behavior. Be wary of extensions with suspiciously perfect ratings or reviews that seem artificially generated. Legitimate extensions typically have a mix of ratings with detailed, specific feedback from real users.

Step 3: Examine permission requests carefully

This is perhaps the most critical step in your assessment. When you click “Add to Chrome,” pay close attention to the permission dialog that appears. Question if the requested permissions make sense for the tool’s functionality and be particularly cautious of extensions requesting broad permissions such as “Read and change all your data on the websites you visit.”

Step 4: Check installation numbers and update history

Extensions with millions of users and regular updates are generally safer bets than those with just a few hundred installations. However, don’t let high installation numbers alone convince you. Look for extensions that receive regular updates, which indicates active maintenance and ongoing security attention from developers.

Step 5: Research recent security issues

Before installing, do a quick web search for the extension name with terms like “security,” “malware,” or “removed.” This will reveal any recent security incidents or concerns that other users have reported. Security researchers and tech blogs often publish warnings about problematic extensions, information that can be invaluable in your decision-making process.

Ongoing browser security

The security landscape changes constantly, and extensions that are safe today might develop problems in the future. This is why ongoing vigilance is just as important as your initial assessment.

• Install only as needed: Adopt a minimalist approach to installing extensions, as every browser extension you add increases your attack surface. Only install those you absolutely need.
• Regularly audit your installed extensions: Set a reminder to review your extensions every few months, removing any that you no longer use or that haven’t been updated recently. This reduces your attack surface and helps keep your browser running efficiently.
• Be wary of unrealistic benefits: When adding new browser extensions, be cautious of those that promise fantastic functions such as dramatically increasing internet speed or providing access to premium content for free. Extensions that require you to create accounts with suspicious email verification processes or that ask for payment information outside of Google’s official channels should also raise red flags.
• Be cautious of duplicate functions: Be suspicious if the extension is replicating functionality already built into Chrome, as these often exist primarily to harvest user data. Extensions with generic names, poor grammar in their descriptions, or unprofessional-looking icons and screenshots indicate lower development standards and potentially higher security risks.
• Install only from official stores: While not perfect, official browser stores offer significantly more security oversight than third-party sources or direct installation methods. Their layers of security screening include automated malware detection, manual code reviews for popular extensions, continuous monitoring for suspicious behavior, review systems, and developer verification processes.
• Enable automatic updates and smart monitoring: Browser updates often include enhanced extension security and additional protection mechanisms that help detect and prevent malicious extension behavior. In addition, implement a monitoring system to identify extensions that update unusually frequently or at suspicious times, such as during periods you’re less likely to notice behavioral changes.
• Deploy comprehensive protections: Integrate your browser extension security with broader security measures that can monitor extension behavior and detect suspicious activities such as unauthorized data access, unexpected network connections, or attempts to modify system files. These tools use behavioral analysis and machine learning to identify malicious patterns that might not be apparent through manual observation.
• Secure your shopping and banking accounts: Your financial transactions and shopping activities represent high-value targets that need specialized protections. Consider using a dedicated browser for financial activities to isolate your transactions or temporarily disable extensions not related to security or privacy. Enable multi-factor authentication to prevent unauthorized access even if a malicious extension captures your primary login credentials.
• Create a positive security routine: Establish straightforward security routines that include the measures listed above to ensure that your shopping, banking, and general browsing activities remain secure while still allowing you to benefit from the enhanced functionality that well-designed extensions provide.

Thankfully, Google continues to improve its security measures for the Chrome Web Store by implementing stricter review processes for extensions and enhancing its ability to detect and remove malicious extensions after they’ve been published. For additional protection, enable Chrome’s Enhanced Safe Browsing, under the browser’s Privacy and Security section.

Malicious browser extensions also pose similar threats across all major browser ecosystems, with attackers targeting the same vulnerabilities: excessive permissions, post-installation payload updates, and social engineering tactics.

Safari’s extension model, while more restrictive, still allows extensions to access browsing data and modify web content when you grant permissions. Microsoft Edge, built on Chromium, shares Chrome’s extension architecture and therefore inherits many of the same security challenges, though Microsoft has implemented additional screening measures for their Edge Add-ons store. Regardless of which browser you use, the fundamental protection strategies remain consistent.

Action plan if you’ve installed a malicious extension

If you suspect you’ve installed a malicious browser extension by mistake, speed matters in the race to protect your accounts. Follow this clear, step-by-step guide to remove the extension, secure your accounts, and check for any signs of compromise.

1. Immediately disconnect sensitive accounts: Sign out of all banking, shopping, and financial accounts you’ve accessed recently. Malicious extensions can capture session tokens and credentials in real-time, making immediate disconnection critical to prevent unauthorized access.
2. Remove the malicious extension completely: Open your browser settings and navigate to the Extensions or Add-ons section. Locate the suspicious extension and click “Remove” or “Uninstall.” Don’t just disable it. Check for related extensions that may have been installed simultaneously, as malicious extensions often come in bundles.
3. Clear all cookies and site data: Go to your browser’s privacy settings and clear all stored cookies, cached data, and site data to remove persistent tracking mechanisms or stored credentials the malicious extension may have accessed or modified. Pay special attention to clearing data from the past 30 days or since you first noticed suspicious activity.
4. Change all your passwords immediately: Start with your most sensitive accounts—banking, email, and work credentials—followed by all other accounts. Use strong, unique passwords that will make it difficult for the malicious extensions to attempt to access your accounts again. As mentioned earlier, enable multi-factor authentication.
5. Run a comprehensive security scan: Use reputable security software such as McAfee+ to perform full system scans on all devices where you’ve accessed sensitive accounts. Because malicious extensions can download additional malware or leave traces, it is best to schedule follow-up scans over the next few days to catch any delayed payloads.
6. Review all account activity thoroughly: Many malicious extensions operate silently for weeks before executing their primary payload. So keep monitoring your login history, transaction records, and changes in account settings across all your accounts, and look for any unauthorized transactions.
7. Set up account alerts: Set up automated account alerts for all transactions and closely monitor your bank and credit card statements for the next 60-90 days. Place fraud alerts with major credit bureaus if you suspect identity information may have been compromised.

Final thoughts

Browser extensions offer great functionality and convenience, but could introduce cybersecurity risks. With the right combination of smart browsing habits, regular security audits, and comprehensive protection tools, and staying informed, you can safely explore the web, manage your finances online, and shop without worry.

Make it a habit to question your intent to install a new extension, and download only from official browser stores. Review your installed extensions monthly—determine if each one still serves your needs. These practices, combined with keeping your browser and operating system updated, and employing trusted security software, reinforce your defense against evolving online threats. Remember to research any new browser extensions thoroughly before installation, checking developer credentials and reading recent user reviews to identify which browser extensions to avoid.

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