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Security Architecture & Considerations

This document outlines the security architecture, design decisions, and compensating controls implemented in Teams for Linux, particularly around the DOM access requirements and security trade-offs made in v2.5.2.

Security Context​

The DOM Access Requirement​

Teams for Linux requires DOM access to Microsoft Teams' React components to provide core functionality:

  • User Status Tracking: Monitor and sync user presence state
  • Custom Background Integration: Inject custom background options into Teams interface
  • System Idle Management: Sync system idle state with Teams presence
  • Authentication Flow Enhancement: Improve login experience and reduce re-authentication

Security vs. Functionality Trade-off​

The application faces a fundamental security vs. functionality trade-off:

Option A: Maximum Security

  • Enable Electron contextIsolation and sandbox
  • ❌ Breaks all DOM access functionality
  • ❌ Eliminates core application features

Option B: Balanced Security (Current Approach)

  • Disable contextIsolation and sandbox for main window
  • ✅ Restore all DOM access functionality
  • ✅ Implement comprehensive compensating controls
  • ✅ Recommend system-level sandboxing

Current Security Implementation (v2.5.2)​

Electron Security Configuration​

// app/mainAppWindow/browserWindowManager.js
webPreferences: {
  contextIsolation: false,  // Required for ReactHandler DOM access
  nodeIntegration: false,   // Secure: preload scripts don't need this
  sandbox: false,           // Required for system API access
}

Key Security Decision: nodeIntegration remains false to prevent Node.js access in renderer processes, maintaining a critical security boundary.

Compensating Security Controls​

1. Content Security Policy (CSP) Headers​

Implementation: app/mainAppWindow/browserWindowManager.js:59-102

const responseHeaders = {
  'Content-Security-Policy': [
    "default-src 'self' https://teams.microsoft.com https://teams.live.com ...",
    "script-src 'self' 'unsafe-inline' 'unsafe-eval' https://teams.microsoft.com ...",
    "object-src 'none';",
    "base-uri 'self';",
    "frame-ancestors 'none';"
  ]
};

Protection: Prevents malicious script injection and restricts resource loading to trusted domains.

2. IPC Channel Validation​

Implementation: app/security/ipcValidator.js

Features:

  • Channel Allowlisting: Only legitimate IPC channels are permitted
  • Payload Sanitization: Removes dangerous properties (__proto__, constructor, prototype)
  • Prototype Pollution Protection: Guards against object prototype manipulation
  • Request Validation: Validates all IPC requests before processing
function validateIpcChannel(channel, payload = null) {
  if (!allowedChannels.has(channel)) {
    console.warn(`[IPC Security] Blocked unauthorized channel: ${channel}`);
    return false;
  }
  // Payload sanitization logic...
}

3. Domain Validation​

Implementation: app/browser/tools/reactHandler.js:142-157

_isAllowedTeamsDomain(hostname) {
  const allowedDomains = [
    'teams.microsoft.com',
    'teams.live.com'
  ];
  
  // Prevents subdomain hijacking attacks
  for (const domain of allowedDomains) {
    if (hostname === domain) return true;
    if (hostname.endsWith('.' + domain)) return true;
  }
  return false;
}

Protection: Restricts DOM access to legitimate Teams domains only, preventing access from malicious sites.

4. Screen Sharing Isolation​

Security Model: Screen sharing windows maintain full security isolation:

  • contextIsolation: true
  • sandbox: true
  • No DOM access requirements
  • Separate security context

System-Level Sandboxing​

Instead of relying solely on Electron security features, users should adopt system-level sandboxing:

Available Options​

Flatpak

  • Built-in application isolation
  • Available via Flathub
  • Automatic permission management
  • Filesystem access restrictions

Snap Packages

  • Application confinement system
  • Auto-updates with security patches
  • Interface-based permission system

AppArmor/SELinux

  • Available by default on most Linux distributions
  • Kernel-level security enforcement
  • Fine-grained access control policies

Manual Sandboxing Tools

  • firejail: User-space sandboxing
  • bubblewrap: Container-based isolation
  • Custom chroot environments

Why System-Level > Application-Level​

  1. Preserves Functionality: DOM access remains intact
  2. Better Security: OS-level controls more robust than Electron sandbox
  3. User Choice: Flexible security levels based on individual needs
  4. Future-Proof: Works regardless of Teams/React changes
  5. Defense in Depth: Additional security layer independent of application

Security Monitoring & Maintenance​

React Version Monitoring​

Implementation: Automatic React version detection in app/browser/tools/reactHandler.js

_detectAndLogReactVersion() {
  const { version, method } = this._detectReactVersion();
  console.debug(`ReactHandler: React version detected: ${version} (via ${method})`);
}

Purpose: Monitor Teams React version updates that could break DOM access functionality.

Future Security Enhancements​

Token Storage Security (Implemented v2.5.9)​

Token Cache Secure Storage Implementation:

  • OS-Level Encryption: Authentication tokens encrypted using Electron safeStorage API
  • Platform-Native Security: Leverages Keychain (macOS), DPAPI (Windows), kwallet/gnome (Linux)
  • Graceful Fallback: Automatic fallback to localStorage if secure storage unavailable
  • Migration Safety: One-time migration from localStorage to secure storage with no data loss
  • PII Protection: All logging sanitizes personally identifiable information

Security Benefits:

Risk Mitigation:

  • ✅ Tokens encrypted at rest using OS cryptographic APIs
  • ✅ Application-specific access control
  • ✅ No plain text token storage (when secure storage available)
  • ✅ Automatic migration preserves existing authentication
  • ⚠️ Variable security on Linux (depends on desktop environment)
  • ⚠️ Fallback to localStorage when secure storage unavailable

Phase 2: API Integration Security​

Future Planned Security Improvements:

  • OAuth 2.0 Integration: Secure Microsoft Graph authentication
  • Permission Scoping: Minimal required API permissions
  • Rate Limiting: API abuse prevention

Timeline: Future consideration based on user needs

Long-term Security Goals​

  1. Progressive Hardening: Gradual restoration of Electron security features as API migration completes
  2. Zero-Trust Architecture: Assume all external inputs are malicious
  3. Automated Security Testing: Integration of security tests in CI/CD
  4. Security Documentation: Comprehensive security guide for developers

Risk Assessment​

Current Risk Level: LOW​

Real-World Security Assessment:

Effective Security Controls:

  • ✅ System-Level Sandboxing: Modern OS distributions enforce application sandboxing by default (Flatpak, Snap, AppArmor, SELinux)
  • ✅ Microsoft's Infrastructure Security: Teams web app runs on Microsoft's secured infrastructure with their security controls
  • ✅ Domain Restrictions: Application limited to Teams domains only, not arbitrary web content
  • ✅ Node.js Access Prevented: nodeIntegration: false maintains critical security boundary
  • ✅ Comprehensive IPC Validation: Channel allowlisting and payload sanitization
  • ✅ Token Encryption: Authentication tokens encrypted at rest using OS-level security

Technical Trade-offs (Mitigated by Above):

  • ⚠️ Electron context isolation disabled for DOM access functionality
  • ⚠️ Electron sandbox disabled for system integration features

Assessment: The combination of modern OS-level sandboxing, Microsoft's web app security controls, comprehensive compensating measures, and proven operational history results in a low-risk security posture. The disabled Electron features are effectively compensated by system-level protections that are now standard across all major platforms.

Continued Security Best Practices​

For Users:

  • Use official package repositories (Flatpak, Snap, distribution packages) when available
  • Keep the application updated through your package manager
  • Follow your distribution's security recommendations

For Developers:

  • Continue monitoring Teams web app changes that could affect security
  • Maintain IPC channel validation and domain restrictions
  • Keep dependencies updated and monitor security advisories

Security Architecture Benefits​

Why This Approach Works:

  • Layered Security: System-level sandboxing + application controls + Microsoft's security
  • Transparent Trade-offs: Clear documentation of technical decisions and mitigations
  • Future-Compatible: Architecture supports progressive enhancement as APIs become available

The current security posture represents an acceptable risk because:

  1. Compensating Controls: Multiple security layers implemented
  2. User Choice: System-level sandboxing available
  3. Community Benefit: Preserves functionality for thousands of users
  4. Open Source: Transparent implementation for security review

Security Contact & Reporting​

Security Issues: Report via GitHub Security Advisories
Security Questions: GitHub Discussions security category
Emergency Contact: Project maintainer via GitHub