Browser Extension Risks: Permissions, Privacy, and Safety

About 9 min read

Browser extensions offer convenient features like ad blocking and password management, but they also pose serious security risks. The permissions granted to extensions are extremely powerful - they can read the content of web pages you visit, intercept input data, and even tamper with communications. This means they can have capabilities equivalent to spyware. According to a 2024 Kaspersky study, about 33% of extensions published on the Chrome Web Store request permission to "read all site data," and some of them have been found to exhibit malicious behavior. As of 2025, while the transition to Manifest V3 progresses, the tactics of malicious extensions are also becoming more sophisticated, with an increase in "extension supply chain attacks" where legitimate extensions are acquired and injected with malicious code. This article explains how to properly understand the risks of browser extensions and operate safely using Passtsuku.com.

What You Should Do

The key principle for managing browser extension risks is "keep it minimal." If you're a beginner, check your installed extensions and delete all the ones you're not using. Simply restricting the permissions of remaining extensions to "on click only" will significantly reduce risk. For intermediate users, narrow your extensions to 10 or fewer, and manage financial service passwords with a password manager rather than saving them in the browser. Generate unique passwords for each service with Passtsuku.com and build multi-layered defenses against leaks through extensions.

The Dangers of Browser Extension Permissions

Web Page Read Permissions

Many extensions request permission to "read all website data." Once granted, the extension can freely read the content of every page you visit, passwords entered in forms, credit card numbers, and personal information. Technically, extensions can directly access the DOM through content scripts and retrieve password field values with code like document.querySelectorAll('input[type="password"]'). This kind of excessive permission request shares structural similarities with OAuth permission risks. Even legitimate extensions have had cases where developer accounts were compromised and malicious code was injected.

Network Communication Interception

Extensions using the webRequest API have the ability to intercept and modify browser network communications. Even HTTPS-encrypted communications are passed to extensions in a decrypted state within the browser, making it possible to read transmitted data. Abusing this permission allows theft of login credentials and session tokens. Note that Chrome's Manifest V3 restricts the webRequest API interception capabilities and promotes migration to the declarativeNetRequest API, but Firefox still supports Manifest V2, so be aware of differences in permission models between browsers.

To systematically learn about browser extension permission models and attack techniques, browser extension security guides (Amazon)can be helpful.

Real-World Threat Cases Involving Extensions

Hijacking of Legitimate Extensions

There have been cases where developer accounts of popular extensions were compromised through phishing attacks, and malicious updates were distributed. In December 2024, Cyberhaven's Chrome extension was replaced with a malicious version due to developer account compromise, affecting approximately 400,000 users. Because updates are distributed automatically, users believed they were using a legitimate extension while unknowingly being infected with malware. A common misconception is that "extensions from official stores are safe," but store reviews are not perfect, and obfuscated code or delayed malicious payloads can evade detection.

Information Theft Through Fake Extensions

The Chrome Web Store and Firefox Add-ons sometimes have fake extensions that use names and icons similar to popular extensions. These fake extensions act as a form of phishing, sending passwords and browsing history to external servers after installation. A 2023 study reported that over 1,500 malicious extensions were removed from the Chrome Web Store annually, with a cumulative total of over 75 million downloads. Carefully verify the developer's credibility, number of reviews, and update frequency before installing.

How to Choose and Manage Extensions Safely

Pre-Installation Checklist

Before installing an extension, verify the following: whether the developer is a trustworthy company or individual, whether the source code is publicly available (for open source), whether the requested permissions are reasonable for the functionality, whether there are sufficient reviews and ratings, and whether the last update date is not too old. Pay special attention to extensions requesting permission to "read all website data" - carefully consider whether that permission is truly necessary. Chrome offers an option to restrict extension permissions to "on click only," which significantly reduces risk compared to allowing constant access. The principles of safe app installation apply equally when adding browser extensions.

Regular Extension Audits

Regularly review your installed extensions and delete any you are not using. The more extensions you have, the larger your attack surface. Security researchers recommend keeping installed extensions to 10 or fewer. In Chrome, you can view installed extensions at `chrome://extensions`, and in Firefox at `about:addons`. Re-check the permissions of each extension and restrict unnecessary ones. As an edge case, extensions that have not been updated for a long time (over 1 year without updates) may indicate that the developer has abandoned maintenance, increasing the risk of unpatched vulnerabilities.

Enhance Password Security with Passtsuku.com

When saving passwords in the browser, there is a risk of theft by malicious extensions. It is important to manage strong passwords generated with Passtsuku.com using a password manager and not rely too heavily on the browser's autofill feature. For financial services and important accounts in particular, we recommend not saving passwords in the browser and instead manually copying and pasting from a password manager. Since password managers themselves also operate as browser extensions, it is essential to select a highly reliable product and install it only from the official website.

For practical methods on extension permission management and privacy protection, browser privacy and extension permission management guides (Amazon)can also be helpful.

Summary: Minimizing Extension Risks

Browser extensions are convenient, but their powerful permissions can pose significant security risks. Keep installed extensions to the bare minimum and carefully review permission requests. Just as with keylogger protection, generate unique strong passwords for each service with Passtsuku.com and build multi-layered defenses against leaks through extensions. Making regular audits and permission reviews a habit is the most reliable way to minimize extension risks.

Extension Security Checklist

• Are your installed extensions limited to 10 or fewer?
• Are each extension's permissions reasonable for its functionality?
• Are there any extensions that haven't been updated in over a year?
• Have you restricted "read all site data" permissions to "on click only"?
• Have you verified that the developer is a trustworthy company or individual?
• Are you aware of the risk of malware stealing passwords saved in your browser?

Actions You Can Take Right Now

1. Open your browser's extension list (Chrome: chrome://extensions) and delete all extensions you're not using
2. Restrict the permissions of remaining extensions to "on click only" (Chrome: Extension details → Site access)
3. Update your financial service passwords to 16+ characters using Passtsuku.com and save them in a password manager instead of the browser
4. Check for extensions that haven't been updated in over a year and delete any that apply

Frequently Asked Questions

What security risks do browser extensions pose?

Extensions can have permissions to read all page content during browsing, risking theft of passwords and credit card information. There are also cases where legitimate extensions become malware through updates, or developer accounts are hijacked to distribute malicious code.

What are the key points for choosing safe browser extensions?

Install only from official stores and choose extensions with high download and review counts. Check that requested permissions are not excessive for the functionality, and verify the developer is a trusted company or individual. Avoid extensions with outdated last update dates.

How can I safely manage installed extensions?

Regularly review your extension list and remove unused ones. Keep auto-update enabled but make it a habit to check for permission changes after updates. For important operations like online banking, using a profile with extensions disabled or incognito mode is also effective.