The Browser Extension - The SoC's Blind Spot

Executive Summary

Browser extensions have become ubiquitous productivity tools, but they also represent one of the most overlooked attack vectors in enterprise security. A recent three-month investigation into browser extension installations across corporate endpoints revealed a concerning pattern: employees routinely installing VPN tools, cryptocurrency wallets, deprecated add-ons, and even compromised extensions—each creating pathways for data exfiltration, credential theft, and security control bypass.

The findings demonstrate that browser extension security is not just an IT policy issue—it’s an active and persistent threat requiring immediate attention.

The Investigation

Over past three months, I’ve analyzed browser-based file creation events, specifically focusing on:

• .crx files (Chrome/Edge/Brave extensions)
• .xpi files (Firefox extensions)

These file creation events indicate when browser extensions are installed or updated on user endpoints. The investigation uncovered multiple categories of high-risk extensions that had been deployed across the organization without proper security review.

What Was Found: A Taxonomy of Risk

Category 1: VPN and Proxy Extensions

The Most Concerning Finding

Multiple employees installed free VPN extensions including:

• Browsec VPN
• NordVPN
• ProtonVPN
• VeePN
• UrbanVPN
• HolaVPN

Example Log Analysis:

File Created: [EXTENSION_ID]_3_92_3_0.crx
Path: C:\Users\[username]\AppData\Local\Temp\chrome_url_fetcher_[pid]\
Extension: Browsec VPN – Free VPN for Chrome
User: [Employee A]
Device: [endpoint-001.corporate.local]

Why This Matters:

VPN extensions fundamentally undermine enterprise security by:

• Bypassing corporate firewalls and proxy controls
• Encrypting outbound traffic, making it invisible to Security Operations Center (SOC) monitoring
• Tunneling data outside organizational visibility, creating blind spots in data loss prevention (DLP)
• Potentially routing traffic through untrusted infrastructure in unknown jurisdictions

When employees use VPN extensions, security teams lose the ability to:

• Detect malware command-and-control traffic
• Monitor for data exfiltration
• Enforce web filtering policies
• Maintain audit trails for compliance

Real-World Impact: If an employee’s machine is compromised, attackers can use the installed VPN extension to exfiltrate data through encrypted channels that bypass all corporate security controls.

Category 2: Cryptocurrency and Web3 Extensions

Example Detected:

• MetaMask (cryptocurrency wallet)
• Xverse: Bitcoin Crypto Wallet
• Zerion Wallet: Crypto & DeFi

Security Implications:

While cryptocurrency extensions may seem benign, they introduce several risks:

• Credential storage vulnerabilities: Crypto wallets store private keys that, if compromised, can result in financial loss
• Phishing target: Attackers specifically target crypto wallet extensions with sophisticated phishing campaigns
• Unapproved financial transactions: Potential for unauthorized use of organizational resources
• Data exposure: Transaction history and wallet addresses can leak organizational relationships

In enterprise environments where cryptocurrency isn’t part of business operations, these extensions serve no legitimate purpose and represent pure risk.

Category 3: Deprecated and Removed Extensions

Critical Discovery:

Extension ID: [EXTENSION_ID]
File: BKKBCGGNHAPDMKELJLODOBBKOPCEICHE_7_8_2_0.crx
Status: NO LONGER AVAILABLE in Chrome Web Store
User: [Employee B]
Device: [endpoint-002.corporate.local]
Installation Method: Side-loaded or retained after removal from store

Why Extensions Get Removed:

When extensions are removed from official stores, it’s often because they:

• Contain malware or malicious code
• Violate privacy policies
• Have been abandoned by developers
• Exhibit exploitable vulnerabilities

The Danger:

Deprecated extensions no longer receive security updates. They become:

• Permanent vulnerabilities in the browser environment
• Exploitation targets for attackers who know they won’t be patched
• Persistence mechanisms for existing compromises

An extension that’s been removed from the store but remains installed is analogous to running unpatched software with known vulnerabilities—except it has deep access to browsing data, cookies, and potentially all website content.

Category 4: Research-Documented Vulnerable Extensions

High-Risk Finding:

Extension: Ad Blocker – Stands AdBlocker
Extension ID: lgblnfidahcdcjddiepkckcfdhpknnjh
Version: 2.1.54.0
User: [Employee B]
Device: [endpoint-002.corporate.local]

Academic Research Evidence:

A 2023 USENIX Security Symposium paper (Kim et al.) specifically identified Stands AdBlocker as exhibiting security weaknesses including:

• Universal Cross-Site Scripting (UXSS) vulnerabilities
• Cross-origin resource access flaws
• Potential for data exfiltration
• Privilege escalation risks

What UXSS Means:

Universal XSS vulnerabilities in browser extensions are particularly dangerous because:

• They bypass the same-origin policy, a fundamental browser security control
• Attackers can inject malicious scripts into ANY website the user visits
• The extension’s elevated privileges allow access to:
  • Authentication cookies
  • Session tokens
  • Form data including passwords
  • All page content across all domains

Translation: An extension with UXSS vulnerabilities essentially gives attackers a keylogger and screen recorder for everything done in the browser.

While the detected version (2.1.54.0) is newer than the study version, the presence of an extension with documented security flaws represents unacceptable risk in enterprise environments.

Category 5: Productivity Tools with Hidden Data Exposure

The Seemingly Innocent Threats

Beyond obviously risky extensions like VPNs, the investigation identified a category that’s particularly insidious: productivity tools that employees install to work more efficiently, not realizing they’re creating massive data exposure risks.

AI Summarizers and Content Processors

Detected patterns included:

• ChatGPT-powered webpage summarizers
• AI reading assistants
• Document analysis extensions

The Risk Profile:

When an employee uses an AI summarizer extension on a confidential internal document:

1. Entire page content is transmitted to external AI service
2. No encryption or data handling guarantees beyond the vendor’s privacy policy
3. Data may be used for model training depending on terms of service
4. No organizational control over data retention or deletion

Real-World Scenario:

Employee views internal financial report in browser
Clicks "Summarize with AI" extension button
Complete document content sent to third-party AI service
Report contains:
  - Unreleased earnings data
  - M&A discussions
  - Strategic initiatives
  - Competitive intelligence
All now outside organizational control

Grammar and Writing Assistants (e.g., Grammarly)

Why Grammarly-Type Extensions Are Particularly Risky:

These extensions operate by:

• Intercepting every keystroke in real-time across all websites
• Transmitting text to external servers for grammar analysis
• Maintaining persistent monitoring of all text input

What Gets Captured:

• Corporate email content (including confidential communications)
• Passwords typed into login forms
• Financial data entered into forms
• Personal health information in medical portals
• Proprietary code and technical documentation
• Internal chat messages and collaboration tool content
• Draft contracts and legal documents

The Technical Reality:

To function, grammar extensions need permission to:

json

{
  "permissions": [
    "activeTab",
    "storage",
    "webRequest",
    "webRequestBlocking"
  ],
  "content_scripts": [{
    "matches": ["<all_urls>"],
    "js": ["content.js"],
    "run_at": "document_start"
  }]
}

This means they can intercept and read content on every website, including:

• Banking portals
• SaaS applications (Salesforce, Workday, ServiceNow)
• Cloud infrastructure consoles (AWS, Azure, GCP)
• Internal web applications
• Email clients
• Document management systems

Screen Recording and Screenshot Extensions

Detected extensions capable of:

• Full-screen recording
• Region-specific screenshots
• Automatic cloud upload of captures

The Exposure:

A single screen recording session can capture:

• Multiple passwords and credentials as they’re entered
• Confidential documents being reviewed
• Internal system interfaces and architecture
• Employee and customer PII
• Financial data and transactions
• Video conference content

The Clipboard Manager Risk:

Extensions that monitor clipboard activity capture:

• Passwords copied from password managers
• Sensitive data copied between applications
• Account numbers and financial information
• API keys and access tokens
• Confidential excerpts from documents

Many clipboard extensions sync history to cloud services, creating a permanent record of everything copied—accessible potentially to:

• The extension developer
• Cloud service provider
• Anyone who compromises the user’s extension account
• Law enforcement or government requests to the service provider

Other High-Risk Extensions Detected

Additional concerning patterns included:

Content Processing Extensions:

• AI Summarizers (ChatGPT-based page summarizers, AI reading assistants)
  • Risk: Send entire webpage content, including confidential documents and internal communications, to external AI services
  • Data exposure: Intellectual property, trade secrets, and sensitive business information transmitted to third-party AI platforms
  • No data retention control or visibility into how information is processed or stored
• Third-Party Article Summarizers (Pocket, Instapaper-type tools)
  • Risk: Content is uploaded to external servers for processing
  • Privacy concern: Reading habits and accessed URLs create detailed intelligence profile
  • Compliance issue: May violate data handling policies by sending regulated information externally
• Grammar and Writing Assistants (Grammarly, similar tools)
  • Risk: Every keystroke in text fields is transmitted to external servers for analysis
  • Critical exposure: Passwords, confidential emails, proprietary documents, financial data, and PII are captured
  • Persistent monitoring: Real-time transmission of all typed content across all websites
  • Data retention: Text data stored on vendor servers with unclear retention policies

Capture and Recording Tools:

• Screen Recording/Screenshot Extensions
  • Risk: Can capture everything displayed on screen, including sensitive data
  • Surveillance concern: May record without clear user awareness
  • Data leakage: Screenshots may be uploaded to cloud services or shared automatically
  • Compliance violation: Recording confidential information or PII without proper controls
• Clipboard Managers
  • Risk: Access to everything copied, including passwords, account numbers, and sensitive data
  • Persistence risk: Clipboard history often synced to cloud services
  • Credential exposure: Commonly used for password management without proper security

    Other High-Risk Extensions Detected

Additional concerning patterns included:

• Pop-up blockers side-loaded from external sources
• Extensions with excessive permission requests
• Add-ons with suspicious update URLs pointing to non-official domains
• Tools requesting access to “all websites” without clear business need

Technical Detection Methodology

File Creation Events:

The investigation leveraged endpoint detection and response (EDR) telemetry to capture file creation events. When a browser installs or updates an extension:

1. The browser downloads a .crx (Chromium) or .xpi (Firefox) package
2. This creates a file creation event in a temporary directory and Downloads directory
3. Security tools can detect this pattern: chrome_url_fetcher_[pid]\[EXTENSION_ID]_[version].crx

Key Detection Points:

Path Pattern: C:\Users\[username]\AppData\Local\Temp\chrome_url_fetcher_*\*.crx
Process: chrome.exe, msedge.exe, brave.exe, firefox.exe
Action: FileCreated
File Type: .crx, .xpi

Limitations Identified:

The investigation noted several important constraints:

• Only new installations or updates were detected - existing extensions that didn’t update during the review period remained invisible
• Brave browser uses non-descriptive naming (e.g., extension_12345.crx), requiring manifest.json analysis for identification
• Multiple browsers (Chrome, Edge, Brave, Firefox, Opera) exist in the environment with varying detection capabilities
• Manual analysis required for extension verification beyond automated detection

Why Browser Extensions Are So Dangerous

1. Excessive Permissions

Many extensions request permissions far beyond their stated functionality:

• Access to “all websites” and ability to “read and modify data”
• Cookie and local storage access
• Clipboard access
• Screenshot capabilities
• Network request interception

Example: An ad blocker legitimately needs to see page content, but it shouldn’t need access to send network requests to arbitrary domains or access clipboard data.

2. Opaque Update Mechanisms

Once installed, extensions can update automatically:

• Updates bypass traditional software approval processes
• Developers can push malicious updates to previously benign extensions
• Corporate security teams often lack visibility into extension updates
• No formal change control or testing process

Real-World Precedent: Multiple legitimate extensions have been sold to malicious actors who then pushed compromised updates to existing users, instantly converting a trusted tool into malware.

3. Persistence and Privilege

Extensions run with elevated privileges within the browser context:

• They persist across browser sessions
• They execute automatically on browser start
• They can intercept and modify all web traffic
• They can access sensitive browser APIs
• They survive system reboots and operate silently

4. Supply Chain Risk

Browser extensions represent a supply chain that’s often completely unvetted:

• Unknown developer backgrounds
• Unclear funding models (especially for “free” VPN services)
• Potential nation-state or criminal ownership
• No code review or security audit requirements
• Terms of service that permit data collection and sharing

5. The Productivity Extension Paradox

The most dangerous extensions are often the ones that seem most helpful:

The Deception:

• Marketed as productivity enhancers
• Offer genuine utility (grammar checking, AI assistance, etc.)
• Users actively want to use them
• Employees resist removal because they’ve become dependent
• Management may not understand the risk

The Reality:

• Grammar checkers = enterprise-wide keyloggers with external data transmission
• AI summarizers = automatic document exfiltration to third-party services
• Screen recorders = visual surveillance tools capturing everything
• Productivity extensions often require the most invasive permissions

Why This Makes Them Dangerous:

1. Security teams hesitate to block them because of business pushback
2. Users install them deliberately and defend their use
3. Data exposure is continuous (not a one-time event)
4. Legitimate functionality masks data collection
5. Terms of service often permit data retention and use

This creates a perfect storm: a tool that users want, that operates with maximum permissions, that continuously transmits sensitive data, and that security teams struggle to eliminate due to perceived business value.

The Broader Security Implications

SOC Visibility Loss

VPN and proxy extensions create a “dark zone” where:

• Encrypted traffic bypasses web proxies
• DLP systems can’t inspect content
• Threat intelligence feeds can’t match IOCs
• Network-based monitoring becomes ineffective

This is equivalent to allowing employees to create encrypted tunnels around all security controls.

Compliance Violations

In regulated industries (healthcare, finance, government), the presence of unapproved extensions can violate:

• Data residency requirements
• Privacy regulations (GDPR, HIPAA)
• Industry standards (PCI-DSS, SOC 2)
• Contractual obligations with clients

Audit Finding Risk: “Organization allows users to install tools that exfiltrate data to third-party services without security review or data processing agreements.”

Incident Response Challenges

When investigating a security incident, browser extensions complicate forensics:

• They can mask attack traffic alongside legitimate extension traffic
• Logs may be incomplete due to VPN encryption
• Attribution becomes difficult when extensions route traffic through shared infrastructure
• Determining what data was exposed requires extension code analysis

Real-World Attack Scenarios

Scenario 1: VPN-Masked Data Exfiltration

1. Attacker compromises employee workstation via phishing
2. Discovers Browsec VPN extension is installed
3. Uses extension to route data exfiltration traffic through VPN
4. Corporate DLP, firewall, and SIEM systems see only encrypted VPN traffic
5. Sensitive data exits the network completely undetected

Scenario 2: Cryptocurrency Extension Phishing

1. Employee has MetaMask installed for personal use
2. Visits work-related website that’s been compromised
3. Attacker serves targeted phishing page mimicking MetaMask interface
4. Employee enters recovery phrase thinking they’re unlocking wallet
5. Attacker gains access to crypto assets, plus potentially:
   • Password reuse insights
   • Personal information
   • Access to any websites where MetaMask was used for authentication

Scenario 3: Deprecated Extension Exploitation

1. Employee installed ad-blocking extension years ago
2. Extension was removed from Chrome Web Store for security issues
3. Extension never updates, contains known UXSS vulnerability
4. Attacker identifies vulnerable extension through browser fingerprinting
5. Exploits UXSS to inject scripts into corporate SaaS applications
6. Harvests authentication tokens and session cookies
7. Gains persistent access to cloud applications

Scenario 4: Malicious Update

1. Popular productivity extension has 100+ employees using it
2. Original developer sells extension to unknown third party
3. New owner pushes update with keylogging functionality
4. All users automatically receive compromised version
5. Corporate credentials and sensitive data exposed before detection

Recommendations and Mitigation Strategies

Immediate Actions

1. Audit Current Extension Deployment

# Example query for EDR telemetry
DeviceFileEvents
| where FileName endswith ".crx" or FileName endswith ".xpi"
| where FolderPath contains "chrome_url_fetcher" 
   or FolderPath contains "firefox\\Profiles"
| summarize Extensions = make_set(FileName) by DeviceName, InitiatingProcessAccountName

Identify:

• All extensions currently in use
• Users with VPN/proxy extensions (immediate priority)
• Deprecated or removed extensions
• Extensions with known vulnerabilities

2. Remove High-Risk Extensions Immediately

Priority removal order:

1. VPN and proxy extensions (Browsec, VeePN, UrbanVPN, etc.)
2. Cryptocurrency wallets (MetaMask, etc.) if not business-related
3. Deprecated extensions no longer in official stores
4. Extensions from academic vulnerability research (Stands AdBlocker, etc.)
5. Extensions with “access all websites” permissions without clear business need

3. Rotate Credentials

For users who had high-risk extensions:

• Force password resets for corporate accounts
• Review access logs for anomalous activity
• Consider sessions compromised and invalidate tokens
• Monitor for account takeover indicators

Policy and Governance

4. Implement Extension Control Policies

Use browser management capabilities to:

Chrome/Edge (Group Policy or Intune):

ExtensionInstallBlocklist: ["*"] (Block all by default)
ExtensionInstallAllowlist: [Approved Extension IDs only]
ExtensionInstallForcelist: [Required business extensions]

Firefox (policies.json):

{
  "policies": {
    "Extensions": {
      "Install": ["approved-extension-id@mozilla.org"],
      "Uninstall": ["malicious-extension-id"],
      "Locked": ["required-extension-id"]
    },
    "ExtensionSettings": {
      "*": {
        "installation_mode": "blocked"
      }
    }
  }
}

5. Create Extension Approval Process

Establish formal process for extension requests:

• Business justification requirement
• Security review checklist
• Privacy impact assessment
• Alternative solution evaluation
• Time-limited approvals with periodic review

6. Block VPN Extensions at Multiple Layers

Don’t rely on policy alone:

• Browser policy blocklists
• Web filtering (block extension store URLs for VPN categories)
• DNS blocking (block known VPN provider domains)
• Network monitoring (alert on VPN protocol detection)

Technical Controls

7. Enhanced Monitoring and Detection

Implement detection rules:

Alert: New Extension Installation
Trigger: FileCreated events with .crx or .xpi in temp directories
Action: Create ticket for security review, alert user's manager

Alert: VPN Extension Detected
Trigger: Extension ID matches known VPN provider list
Action: Immediate alert, auto-block if possible, mandatory removal

Alert: Deprecated Extension Activity
Trigger: Extension ID not found in current store database
Action: Flag for review and removal

Alert: High-Privilege Extension
Trigger: Extension manifest requests "all websites" permission
Action: Security review required

8. Leverage Browser Native Security Features

• Enable Enhanced Safe Browsing (Chrome/Edge)
• Enable extension content verification
• Disable developer mode (prevents side-loading)
• Enable extension sync only with approved corporate account
• Disable inline installation from websites

9. Implement Application Control

Consider application control solutions that:

• Track browser extension installations
• Block unapproved extension execution
• Provide central visibility into all installed extensions
• Enforce allowlist-based extension control
• Alert on policy violations in real-time

User Education and Awareness

10. Security Awareness Training

Educate users on:

• Why extensions are risky: Real examples of compromised extensions
• Permission awareness: What “read and modify all data” actually means
• VPN risks: How they bypass security controls and why they’re prohibited
• Crypto extension risks: Phishing and credential theft scenarios
• Grammar extension dangers: Every keystroke transmitted to external servers
• AI summarizer risks: Entire documents sent to third-party AI services
• Screen recorder risks: Capturing sensitive information including credentials
• The “free” tool trap: How “free” extensions monetize through data collection
• Approval process: How to request legitimate business extensions
• Alternatives: Approved corporate tools that meet the same needs securely

Training Scenarios:

• Show side-by-side comparison of VPN’d vs. non-VPN’d traffic visibility
• Demonstrate how a malicious extension can capture passwords in real-time
• Display what a grammar extension sees when you type an email
• Show AI summarizer sending a confidential document to external service
• Walk through a real incident where an extension was compromised
• Explain compliance implications in simple terms
• Demonstrate screen recorder capturing login credentials

11. Create Secure Alternatives

If users have legitimate needs:

• For ad-blocking: Provide approved ad-blocking (corporate-managed uBlock Origin with allowlist)
• For VPN access: Deploy corporate VPN solution for remote access needs
• For password management: Offer approved password manager extensions (1Password Enterprise, LastPass Enterprise)
• For grammar checking:
  • Deploy Microsoft Editor (for M365 environments) with enterprise controls
  • Use desktop applications instead of browser extensions where possible
  • Provide approved grammar tools with proper data processing agreements
• For AI assistance:
  • Deploy enterprise AI solutions (Microsoft Copilot, Google Duet AI) with data residency controls
  • Create internal AI chatbots for common queries
  • Establish approved AI platforms with proper security review
• For screen capture:
  • Use operating system native tools (Windows Snipping Tool, macOS Screenshot)
  • Deploy approved enterprise screen capture tools with DLP integration
• For content summarization:
  • Provide access to approved AI platforms for document summarization
  • Use native features in Microsoft 365 or Google Workspace
• Create curated list of vetted productivity extensions with documented risk assessments

Ongoing Management

12. Regular Extension Audits

Schedule recurring reviews:

• Monthly: Review new extension installations
• Quarterly: Audit all deployed extensions against current threat intelligence
• Annually: Full review of extension approval policy and allowlist

13. Threat Intelligence Integration

Monitor sources for extension-related threats:

• Chrome Web Store security bulletins
• Academic security research (USENIX, Black Hat, etc.)
• Security vendor advisories
• Browser vendor security blogs
• Extension-specific vulnerability databases

14. Manifest.json Analysis

For Brave and other obfuscated cases:

• Extract manifest.json from extension packages
• Review requested permissions
• Validate update URLs
• Check background scripts
• Analyze content security policies

Measuring Success

Track these metrics to measure program effectiveness:

Reduction Metrics:

• Number of unapproved extensions (target: 0)
• VPN/proxy extension instances (target: 0)
• Deprecated extension count (target: 0)
• High-risk permission grants (target: defined threshold)

Process Metrics:

• Time to detect new extension installation
• Time to review and approve legitimate requests
• Extension audit frequency
• User training completion rates

Incident Metrics:

• Extension-related security incidents
• Policy violation detections
• Attempted VPN extension installations
• Successful blocks via technical controls

The Bigger Picture: Browser Security Strategy

Browser extension control should be part of a comprehensive browser security strategy:

1. Endpoint security - EDR monitoring for malicious extension behavior
2. Network security - Detection of extension-based exfiltration attempts
3. Identity security - Protect credentials from extension-based theft
4. Data security - DLP integration to detect data access by extensions
5. Cloud security - Monitor SaaS app access patterns for extension-based anomalies

Conclusion

The investigation revealed that browser extensions represent a significant and underestimated threat vector in enterprise environments. From VPN tools that completely bypass security controls, to deprecated extensions with known vulnerabilities, to research-documented vulnerable add-ons, the findings demonstrate that uncontrolled browser extensions create multiple pathways for data loss, credential theft, and security control circumvention.

The solution requires a multi-layered approach:

• Immediate action to remove high-risk extensions
• Technical controls to prevent future unauthorized installations
• Policy frameworks to manage exceptions appropriately
• User education to build awareness of risks
• Ongoing monitoring to maintain security posture

Browser extensions won’t disappear—they’re too useful. But organizations can and must bring them under control through the same rigorous change management and security review processes applied to traditional software.

The question isn’t whether you have unauthorized or dangerous browser extensions in your environment. Based on this research, you almost certainly do. The question is whether you’ll discover them proactively through controlled audits, or reactively during a security incident.

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Note: This analysis is based on real security research spanning a three-month investigation period. All usernames, device names, domains, and organizational identifiers have been anonymized to protect privacy while preserving the educational value of the findings.

Call to Action: Start your browser extension audit today. Begin with a simple query in your EDR platform for .crx and .xpi file creation events. You may be surprised by what you find. Then move quickly to implement controls—this is a known threat vector that’s actively exploited, and every day of delay increases risk.

What about File Deletion events

If someone tells or asks to check for file deletion events means, reply them like “Checking for .crx deletion events is like monitoring for the deletion of an Amazon delivery box after you’ve already received the package. The box is gone, but your questionable impulse purchase is sitting right there in your living room. The presence of the .crx file in the temp folder is literally the evidence that the extension is now installed or updated and operational in the browser. Monitoring deletion events would only tell us that Chrome’s normal cleanup process occurred after installation was already complete. after the fact… when it’s already too late… telling you that Chrome successfully deleted a temp file. Congratulations, you’ve reinvented log spam. The security value is in detecting the installation attempt, not confirming that temporary files were subsequently cleaned up as designed.”