Browser Extension Security Risks: 5 Dangers to Check Before Installing (2026)

Browser extensions are incredibly useful—ad blockers, password managers, productivity tools. But they're also one of the biggest security blind spots for most users.

The problem? Extensions can see everything you do in your browser. Every page you visit, every form you fill, every password you type. That's a lot of trust to place in software you probably installed without a second thought.

Here's what you need to know to stay safe.

The 5 security risks of browser extensions

1. Excessive permissions

When you install an extension, it requests permissions. Many users click "Add" without reading them.

Red flag: If a simple utility extension requests permission to "read all your data on all websites," ask why it needs that.

2. Supply chain attacks

In 2024-2025, attackers increasingly targeted browser extensions:

• Cyberhaven breach (December 2024): Attackers compromised the developer's Chrome Web Store account and pushed a malicious update to 400,000+ users
• Multiple Chrome extensions hijacked: Over 30 extensions were compromised in a coordinated campaign
• npm-style attacks: Attackers buy or steal extension developer accounts, then push malicious updates

The scary part? You install a legitimate extension, use it for months, then a malicious update arrives automatically.

3. Data exfiltration

Malicious or compromised extensions can:

• Capture every keystroke (including passwords)
• Screenshot sensitive pages
• Steal session cookies (bypassing 2FA)
• Send data to remote servers

Even "legitimate" extensions sometimes collect more data than necessary. Free extensions often monetize through data collection.

4. Man-in-the-browser attacks

Extensions can modify web pages in real-time. A malicious extension could:

• Change bank account numbers on payment pages
• Inject fake login forms to steal credentials
• Add invisible tracking scripts
• Redirect you to phishing sites

You'd never know the page was modified.

5. Abandoned extensions

Extensions get abandoned all the time. The risks:

• No security updates when vulnerabilities are discovered
• Developer accounts can be sold or stolen
• Chrome may eventually remove them, but not always quickly

How to evaluate browser extension security

Check the permissions

Before installing, review what the extension requests:

Acceptable for password managers:

• "Read and change your data on specific sites" (for autofill)
• "Access your data for sites in the allowlist"

Questionable:

• "Read and change ALL your data on ALL websites" (only if truly necessary)
• "Manage your downloads"
• "Access your tabs"

Red flags:

• Permissions that don't match the extension's purpose
• Vague descriptions of why permissions are needed

Check the developer

Check the reviews and history

• User count: More users = more scrutiny (usually)
• Recent reviews: Look for security complaints
• Update frequency: Regular updates suggest active maintenance
• Age: Brand new extensions are riskier

Check if it's open source

Open source extensions can be audited by security researchers. Major password managers like Bitwarden are fully open source. If an extension handles sensitive data, open source is preferable.

Password manager extensions: specific concerns

Password manager extensions are high-value targets because they handle credentials. Here's what to look for:

Good security practices

• Zero-knowledge architecture: The company can't see your passwords
• End-to-end encryption: Passwords encrypted before leaving your device
• Regular security audits: Third-party penetration testing
• Bug bounty programs: Paying researchers to find vulnerabilities
• Minimal permissions: Only requests what's truly necessary

Warning signs

• No encryption details published
• No security audit history
• Excessive permissions beyond autofill
• Data stored unencrypted locally
• No 2FA option for the vault

What happened in recent extension attacks

Cyberhaven attack (December 2024)

A phishing email compromised a developer's Google account. Attackers pushed a malicious update that:

1. Captured Facebook session cookies
2. Stole Facebook Ads credentials
3. Exfiltrated data to attacker-controlled servers

400,000+ users received the malicious update before it was caught.

Lessons learned

• Even legitimate extensions can be compromised
• Automatic updates are a double-edged sword
• Developer account security matters as much as code security

How to protect yourself

1. Audit your current extensions

Open your browser's extension page and review:

• Do you still use each extension?
• Do the permissions still make sense?
• When was it last updated?

Remove anything you don't actively need.

2. Limit extension count

Every extension is potential attack surface. The fewer you have, the lower your risk.

3. Use extensions from known sources

Stick to extensions from:

• Companies with established reputations
• Open source projects with active communities
• Developers with verifiable identities

4. Review permissions after updates

Major updates can request new permissions. Pay attention to update notifications.

5. Consider alternatives

For high-security tasks, consider whether you need an extension at all:

• Password managers: Desktop apps often have better security isolation than extensions
• Ad blocking: Some browsers have built-in blocking
• Productivity tools: Native apps may be safer than extensions

Our approach at Dosel

We offer both a desktop app and browser integration. Here's how we think about the tradeoffs:

Desktop app (primary):

• Passwords never leave your machine
• No browser extension attack surface
• Full isolation from web content

Browser integration (optional):

• Uses native messaging (more secure than content scripts)
• Minimal permissions
• Credentials injected securely, not read from pages

We believe the desktop-first approach is more secure for credential management. Extensions are convenient, but convenience shouldn't come at the cost of security.

Frequently asked questions

Should I stop using browser extensions entirely?

No—just be selective. Extensions from reputable sources with appropriate permissions are generally safe. The risk is installing too many extensions without evaluating them.

Are Chrome extensions safer than Firefox?

Both have security review processes, but neither catches everything. Chrome's Manifest V3 restrictions improve security but aren't a complete solution. Evaluate each extension individually.

How do I know if an extension has been compromised?

Watch for:

• Unexpected permission requests
• Browser slowdowns
• Strange network activity
• Security software alerts

If concerned, disable the extension and check for news about compromises.

Is it safer to use a password manager's desktop app instead of its extension?

Generally yes, for maximum security. Desktop apps have better process isolation. However, well-designed extensions from reputable password managers (1Password, Bitwarden, Dashlane) are still quite secure.

Key takeaways

1. Review permissions before installing any extension
2. Fewer extensions = smaller attack surface
3. Reputable developers with security track records are safer
4. Open source allows community security audits
5. Desktop apps offer better isolation for sensitive tasks

Browser extensions aren't inherently dangerous—but they require the same scrutiny you'd give any software with access to your sensitive data.

Download Dosel → — 5 free automated password changes per month, no credit card required.

Sources

• Cyberhaven Chrome Extension Compromise - BleepingComputer
• Chrome Extension Security Best Practices - Google
• Browser Extension Security - OWASP

Questions about browser extension security? Reach out at hello@dosel.app.