Malicious Browser Extensions: The Silent Threat to Your Banking and Data Security

That small icon sitting quietly on your browser toolbar might be doing far more than it promises. From reading emails and capturing keystrokes to redirecting bank transactions, malicious browser extensions have emerged as a stealthy but serious digital threat, exploiting the trust users place in everyday online tools. In this edition of The Safe Side, we explore how these extensions work, the warning signs to watch for, and how users can stay protected.

What Are Browser Extensions and How Do They Become Dangerous?

Browser extensions are small add-on tools that people install on web browsers to make everyday tasks easier, such as blocking ads, checking grammar, downloading files, or improving productivity. While many are genuine, some are created with malicious intent or turn dangerous after updates or changes in ownership.

Vaibhav Koul, managing director at Protiviti India Member Pvt. Ltd, explains: "Once installed, an extension operates inside the browser and can see much of what a user does online. They run quietly in the background, often with access to sensitive user data, making malicious add-ons difficult to detect until damage is done."

Zakir Hussain Rangwala, CEO of BD Software Distribution Pvt Ltd, adds: "Some extensions ask for more access than they really need. This can allow them to track browsing activity, view sensitive information, or change website content. Malicious or compromised extensions may misuse this access to steal data, redirect users to unsafe sites, or run hidden scripts."

How Malicious Extensions Misuse Permissions

Vijender Yadav, CEO of Accops, details the risks: "Extensions with clipboard access can monitor sensitive data like passwords or API keys that users copy and paste. Similarly, the 'access to all websites' permission allows an extension to act as a 'Man-in-the-Browser', injecting scripts to scrape corporate data from any active page window."

Rangwala further warns: "Some extensions hide tracking code or activate data collection only after updates, making them hard to detect. Others may access saved passwords, login sessions, or copied text if they have permission, putting personal or company data at risk."

Yadav notes that traditional antivirus software often fails to detect these threats: "Browser extensions don't work like normal files. They run inside the browser itself, using trusted system processes. Because of this, many malicious extensions go undetected."

Organizational Risks and Proactive Controls

Sanjay Mishra, CEO and founder of Reveal Affirm Testify Pvt Ltd, who works with the cyber cell of Uttar Pradesh police, emphasizes: "From a forensic and risk-assessment standpoint, even a single compromised endpoint can act as an effective entry point for wider organizational compromise. Such threats are particularly difficult to detect, as malicious extensions often masquerade as legitimate tools."

He recommends a layered approach: "In addition to user awareness, strict enforcement of browser extension hygiene should be implemented through technical and administrative controls, such as restricting installation privileges, allowing extensions only from approved repositories, and conducting periodic audits."

Expert-Recommended Precautionary Measures

Cybersecurity experts suggest following these precautionary measures while downloading extensions:

Install browser extensions only if they are approved by your company's IT or security team.
Download extensions exclusively from official browser stores, never from pop-ups, ads, or unknown links.
Check the permissions an extension requests and avoid those asking for access unrelated to their purpose.
Review the developer's information, update frequency, and user reviews before installation.
Avoid extensions that promise unrealistic results or pressure you into granting immediate access.
Refrain from installing personal or non-work extensions on office systems used for sensitive tasks.
Remember that even popular extensions can become risky through hidden background updates.
Keep only necessary extensions and regularly remove those you no longer use.
Maintain updated browsers and report unusual behavior like pop-ups or redirects to IT immediately.

For organizations, additional measures include:

Shift towards Managed Enterprise Browsing with centrally controlled browsers and extensions.
Limit or block third-party extensions, allowing only vetted, business-essential tools.
Use security-first browser environments to reduce data leakage risks for employees and contractors.

Red Flags to Watch For

According to Vaibhav Koul, users should be alert to these warning signs:

Extensions requesting permissions unrelated to their stated purpose.
Sudden appearance of pop-ups, ads, or alerts after installation.
Frequent or unexplained updates without clear change details.
Noticeable browser slowdowns or crashes.
Redirects to unknown or suspicious websites.
Extensions lacking clear developer or company information.
Reviews that appear overly positive, repetitive, or potentially fake.
Extensions that disappear from stores and reappear under new names to hide past complaints.

Immediate Steps If You Suspect Compromise

If you suspect your device has been compromised by a malicious browser extension, experts recommend taking these steps immediately:

Remove the suspicious extension from your browser immediately. Consider disabling all extensions first, then re-enabling only trusted ones.
Inform your IT or security team promptly, especially if using a work device. Avoid attempting fixes independently.
Change passwords for accounts accessed through the browser, prioritizing email, work tools, banking, and social media.
Log out of all active sessions on important accounts to block unauthorized access.
Run a full security scan using company-approved antivirus or endpoint security tools.
Check browser settings for unauthorized changes to homepage, default search engine, or proxy settings, and reset as needed.
Clear browser data including cookies, cache, and stored sessions to remove tracking or injected scripts.
Monitor accounts closely for suspicious logins, transactions, or messages in subsequent days.
Report the malicious extension to the official browser store to warn other users.
Avoid reinstalling extensions until the system is cleared and approved by IT professionals.

If your data is compromised, you can register a case either at 1930 or your nearest police station. Acting quickly helps limit damage and prevents further data theft.

The Need for Vigilance in the Digital Age

Browser extensions may appear harmless, but they operate with significant access to users' online activities. As cybercriminals grow more sophisticated, relying solely on basic checks and traditional security tools is insufficient. Employee awareness combined with stronger organizational controls like managed enterprise browsing has become essential.

Treating browser extensions with the same caution as any other software is crucial for reducing data leakage, financial loss, and long-term security risks. In our evolving digital landscape, staying informed and vigilant remains the best defense against emerging cyber threats.