Browser extensions can add useful features to Chrome, Edge, Firefox, and other browsers, but they can also become a major security risk if malicious code is introduced through fake extensions, compromised developer accounts, or malicious updates.
Recent cyberattacks have increasingly targeted trusted software ecosystems, including browser extensions, Visual Studio Code extensions, npm packages, and developer tooling. In some cases, attackers have used malicious updates to steal passwords, session cookies, cryptocurrency wallets, authentication tokens, and browsing data.
This guide explains how malicious browser extensions work, warning signs to watch for, and how to reduce your risk.
Why browser extensions can be dangerous
Many browser extensions operate with broad permissions that allow them to:
- Read and modify website data
- Access cookies and session information
- Inject scripts into webpages
- Monitor browsing activity
- Capture form submissions
- Redirect traffic
- Access clipboard contents
If attackers compromise an extension developer account or publish a malicious extension disguised as a legitimate tool, those permissions can potentially be abused to steal sensitive information from users.
In some recent supply chain attacks, malicious updates were pushed through trusted software ecosystems after developer credentials were compromised.
Common signs an extension may be malicious
Not every suspicious extension is actively malicious, but the following warning signs should be treated seriously.
1. The extension requests excessive permissions
Be cautious if a simple extension requests access that does not match its purpose.
For example:
- A calculator extension should not need access to all website data
- A wallpaper extension should not need clipboard access
- A coupon extension should not require access to passwords or browsing sessions
Review requested permissions before installing extensions.
2. The extension suddenly changes behavior
Malicious activity is sometimes introduced through updates after an extension has already built trust and accumulated users.
Warning signs may include:
- New permissions appearing after updates
- Browser slowdowns
- Unexpected popups or ads
- Redirects to unfamiliar websites
- Search engine changes
- Random tabs opening automatically
3. The developer information looks suspicious
Attackers frequently publish fake extensions designed to imitate legitimate tools.
Look for:
- Misspelled developer names
- Recently created publisher accounts
- Poor grammar or vague descriptions
- Fake AI branding or cloned logos
- Very few reviews or suspiciously repetitive reviews
4. The extension promises unrealistic functionality
Be skeptical of extensions claiming they can:
- Hack social media accounts
- Generate free cryptocurrency
- Bypass security systems
- Unlock premium services illegally
- Automatically make money online
Many of these extensions are scams or malware delivery mechanisms.
5. Security researchers or browser stores flag the extension
Sometimes malicious extensions are removed from browser stores after researchers discover suspicious behavior.
If an extension suddenly disappears from the Chrome Web Store or Firefox Add-ons marketplace, that can be a major warning sign.
How attackers use malicious extensions
Modern malicious extensions are often designed to steal highly valuable data including:
- Passwords
- Session cookies
- Authentication tokens
- Cryptocurrency wallet information
- Email access
- GitHub credentials
- Cloud platform tokens
- Stored browser autofill data
In some cases, attackers use stolen session cookies to bypass passwords and even multi-factor authentication.
Developer-focused extensions can be especially dangerous because they may have access to repositories, CI/CD workflows, cloud infrastructure, API keys, and internal systems.
How to check your installed extensions
Review your installed browser extensions regularly.
In Chrome and Chromium-based browsers:
- Open Chrome
- Click the three-dot menu
- Select Extensions → Manage Extensions
In Firefox:
- Open Firefox
- Open the menu
- Select Add-ons and Themes
Remove extensions you:
- Do not recognize
- No longer use
- Installed temporarily
- Cannot verify as legitimate
How to reduce your risk
To lower the risk of malicious extensions:
- Install as few extensions as possible
- Only use extensions from trusted developers
- Review permissions carefully
- Regularly audit installed extensions
- Remove unused extensions
- Keep browsers updated
- Use multi-factor authentication whenever possible
- Avoid downloading extensions from unofficial websites
Developers should be especially cautious
Developers, administrators, and cryptocurrency users are increasingly being targeted through browser extensions and developer tooling.
Compromised extensions can potentially expose:
- GitHub accounts
- Cloud credentials
- Production environments
- API keys
- SSH keys
- Internal repositories
Several recent supply chain incidents covered by BreachNews involved attackers abusing trusted software ecosystems and developer environments to gain broader access to organizations.
Final thoughts
Browser extensions are often treated as harmless productivity tools, but they can carry significant security risks if malicious code is introduced through fake listings, compromised developer accounts, or malicious updates.
As attackers continue targeting trusted software ecosystems, carefully reviewing and limiting browser extensions has become an increasingly important part of personal and organizational cybersecurity.
