Browser extensions add functionality but can also introduce significant security risks. Understand the dangers of malicious extensions and how to manage them safely.
Browser extensions are one of the most underappreciated security risks in business environments. They are small, they seem harmless, and they often provide genuine value — ad blockers, password managers, grammar checkers, productivity tools. But they also represent a significant attack surface that most organisations do not actively manage.
What Browser Extensions Can Actually Do
Understanding the risk requires understanding the permissions browser extensions operate with. A browser extension, once installed, can:
- Read and modify all data on websites you visit: This includes form fields, login credentials, credit card numbers, and any text you type in the browser.
- Read your browsing history: Where you go online, what you search for.
- Intercept and modify network requests: An extension can see all traffic between your browser and the internet — and in some cases, modify it.
- Access clipboard content: Anything you copy and paste.
- Access local files (with appropriate permissions): Some extensions can read files on your device.
This is not theoretical capability. These are the actual permissions that many widely-used extensions request — and that users click through without reading.
The Threat Landscape
Malicious Extensions From the Start
Extensions in the Chrome Web Store, Firefox Add-ons, and Edge Add-ons undergo some review, but not enough to catch everything. Malicious extensions do appear in official stores before being detected and removed. These are designed from the outset to steal data — typically credentials, session cookies, or financial information.
Legitimate Extensions That Go Rogue
Extensions can be sold, transferred, or compromised by attackers. An extension with a large user base is a valuable target. Numerous documented cases exist of popular, legitimate extensions being acquired and then updated with malicious code. Users who trusted the extension when it was benign continue using it after the code change.
Extensions With Excessive Permissions
Many extensions request far more permissions than their stated functionality requires. A colour picker that requests access to “all website data” is a red flag — a colour picker does not need to read your browsing activity.
Supply Chain Attacks Via Extensions
Extensions that integrate with business tools — CRM connectors, productivity apps, email tools — can be entry points for supply chain attacks. If the extension vendor is compromised, every organisation using that extension is potentially exposed.
Real-World Impact
The consequences of a malicious or compromised extension include:
- Credential theft: Session hijacking allows attackers to access authenticated sessions without needing your password.
- Financial fraud: Extensions that modify banking sites or intercept payment data are documented and active.
- Data exfiltration: Extensions with access to email and document sites can quietly exfiltrate sensitive information.
- Cryptojacking: Some malicious extensions use browser compute resources for cryptocurrency mining.
Managing Browser Extension Risk
Establish an Approved Extensions Policy
For businesses, the most effective control is a managed browser environment with an approved extensions list. Via Microsoft Intune or Group Policy (for Chromium-based browsers on Windows), IT administrators can:
- Block all extensions not on the approved list
- Pre-install approved extensions
- Prevent users from installing extensions without IT approval
This requires effort to set up but eliminates the risk of unsanctioned extensions entirely.
Conduct an Extension Audit
If you do not currently manage browser extensions, start with an audit. Ask staff to list the extensions they have installed. Review each one for:
- Who the developer is (can you verify this is a legitimate organisation?)
- What permissions it requests
- When it was last updated
- Whether it is necessary for the role
Remove anything that cannot be justified.
Evaluate Permissions Before Installing
When installing an extension, Chrome and Edge display the permissions it requires. An extension that requests access to all websites should require a strong justification.
Lower risk permissions: Access to a specific website, access to browser storage, display notifications.
Higher risk permissions: Access to all websites, modify browser settings, read browsing history.
Keep Extensions Updated
Extension developers release security updates. Ensure browser auto-update is enabled so extensions receive patches promptly. But also be alert: a sudden permission change in an extension update (requesting new, broader permissions) is a warning sign.
Password Manager Exception
Password manager extensions (Bitwarden, 1Password, LastPass) inherently require broad access to websites to function — they need to fill credentials across all sites. This is a legitimate exception to the “be wary of extensions requesting all-website access” rule, provided you use a reputable, well-audited password manager from a credible vendor.
Building Browser Security Into Your IT Policy
CX IT Services helps Melbourne businesses implement managed browser policies via Microsoft Intune as part of our endpoint management service. If your organisation currently has unmanaged browser extension use across your team, contact us to discuss how to close this gap.
