This document outlines the security features, best practices, and considerations for the CSC Signature Overlay Tool.

1. Security Overview
2. Input Validation
3. File Upload Security
4. Data Storage Security
5. XSS Protection
6. Memory Management
7. Error Handling
8. Best Practices
9. Security Checklist
10. Incident Response

The CSC Signature Overlay Tool implements a client-side security model with the following principles:

• Defense in Depth: Multiple layers of validation and sanitization
• Principle of Least Privilege: Minimal permissions and access rights
• Fail Secure: Graceful degradation when security checks fail
• Input Validation: All user inputs are validated and sanitized
• No External Dependencies: Self-contained application reduces attack surface
• Recent Security Enhancements (2025): Fixed critical XSS vulnerabilities, enhanced input sanitization, improved error handling

Primary threats addressed:

• Malicious File Uploads: Harmful files disguised as images
• Cross-Site Scripting (XSS): Injection of malicious scripts
• Memory Exhaustion: Resource consumption attacks
• Data Injection: Malicious data in localStorage
• Path Traversal: Unauthorized file system access attempts

All numeric inputs are validated using the validateNumericInput() method:

validateNumericInput(value, min, max, defaultValue)

Security Features:

• Type checking (parseFloat() with isNaN() validation)
• Range clamping (Math.max(min, Math.min(max, num)))
• Default fallback for invalid inputs
• Protection against NaN, Infinity, and negative zero

Protected Inputs:

• Scale values: 10-200%
• Rotation values: -180° to 180°
• Opacity values: 0-100%
• Brush size: 1-20 pixels

String inputs are sanitized using validateStringInput():

validateStringInput(value, maxLength = 100)

Security Features:

• Type verification
• Length limiting (default 100 characters)
• HTML entity encoding
• Removal of dangerous characters: <>"'&

Color values are validated with validateColorInput():

validateColorInput(color)

Security Features:

• Hex color pattern validation: /^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/
• Default fallback to #ffffff
• Protection against CSS injection

Team prefixes and asset types are validated against whitelists:

validateTeamPrefix(prefix)  // Checks against TEAMS array
validateAssetType(asset)    // Checks against ASSET_TYPES keys

Strict MIME type validation with whitelist approach:

const allowedTypes = [
  'image/jpeg', 'image/jpg', 'image/png',
  'image/gif', 'image/webp', 'image/bmp'
];

Security Features:

• MIME type checking (file.type)
• File extension validation (/\.(jpg|jpeg|png|gif|webp|bmp)$/i)
• Double validation (MIME + extension)
• Case-insensitive extension matching

Multiple size restrictions prevent resource exhaustion:

// File upload limits
maxSize: 5 * 1024 * 1024,     // 5MB maximum
minSize: 100,                  // 100 bytes minimum

// Data URL limits
dataUrlLimit: 10 * 1024 * 1024, // 10MB for data URLs

File names are validated to prevent path traversal attacks:

// Blocked patterns
fileName.includes('..')  // Parent directory
fileName.includes('/')   // Unix path separator
fileName.includes('\\')  // Windows path separator

• Timeout Protection: 30-second timeout for file operations
• Memory Limits: Image dimension validation (4096×4096 max)
• Secure Loading: CORS handling for external resources
• Error Handling: Graceful failure for malformed files

All localStorage operations include security validation:

// Safe JSON parsing
safeParseJSON(jsonString) {
  try {
    return JSON.parse(jsonString);
  } catch (error) {
    throw new Error('Invalid JSON format');
  }
}

Stored data is sanitized before persistence:

// Project data sanitization
sanitizeState(state)          // Application state
sanitizeSignature(signature)  // Signature data URLs
sanitizeProjectName(name)     // Project names

Sanitization Features:

• Whitelist allowed object keys
• String length limits
• Data URL format validation
• Size limits for stored data

Prevent storage exhaustion attacks:

maxProjects: 10,                    // Maximum stored projects
maxDataSize: 10 * 1024 * 1024,     // 10MB total limit
maxProjectSize: 5 * 1024 * 1024,   // 5MB per project

Loaded data structure is validated:

validateLoadedProject(project) {
  return project &&
         typeof project.id === 'string' &&
         typeof project.name === 'string' &&
         typeof project.timestamp === 'number' &&
         // ... additional checks
}

• textContent Usage: DOM text insertion uses textContent instead of innerHTML
• Attribute Validation: All dynamic attributes are validated
• HTML Encoding: User input is HTML-encoded before display

Toast messages are XSS-protected:

showToast(message, type, duration) {
  const sanitizedMessage = this.sanitizeText(message);
  toast.textContent = sanitizedMessage;  // Safe insertion
}

All dynamically generated content is sanitized using improved methods:

// Fixed sanitization method (2025 update)
sanitizeText(input) {
  const div = document.createElement('div');
  div.textContent = String(input || '');
  return div.textContent;  // Returns safe text content
}

// HTML encoding when needed
encodeHtml(input) {
  const div = document.createElement('div');
  div.textContent = String(input || '');
  return div.innerHTML;  // Returns HTML-encoded content
}

Security Improvements (2025):

• Fixed critical XSS vulnerability in error handling (replaced innerHTML with DOM creation)
• Enhanced text sanitization methods for proper XSS protection
• Added strict base64 validation for data URLs
• Implemented generic error handling wrapper to reduce code duplication

Automatic memory usage monitoring:

performanceMonitor() {
  if (performance.memory && memory.usedJSHeapSize > 50 * 1024 * 1024) {
    console.warn('High memory usage detected');
  }
}

Monitoring Features:

• 30-second monitoring intervals
• 50MB usage threshold
• Automatic cleanup recommendations
• Memory leak detection

Systematic resource management:

cleanup() {
  // Clear timeouts/intervals
  clearInterval(this.performanceInterval);
  
  // Clear canvas contexts
  this.canvas.clear();
  this.canvas.clearDrawing();
  
  // Reset application state
  this.state = { ...DEFAULT_STATE };
}

• Object Nullification: Explicit null assignment for large objects
• Event Listener Cleanup: Proper removal of event listeners
• Canvas Cleanup: Regular canvas context clearing

Comprehensive error catching:

// Synchronous errors
window.addEventListener('error', (event) => {
  console.error('Application error:', event.error);
  Utils.showToast('An error occurred. Please refresh.', 'error');
});

// Asynchronous errors
window.addEventListener('unhandledrejection', (event) => {
  console.error('Unhandled promise rejection:', event.reason);
  Utils.showToast('An error occurred. Please try again.', 'error');
});

Error messages are sanitized to prevent information leakage:

• Generic Messages: Avoid exposing internal details
• User-Friendly: Provide actionable guidance
• Logging: Detailed errors logged to console for debugging
• No Stack Traces: Stack traces not exposed to users

All async operations have timeout protection:

// Image loading timeout
const timeout = setTimeout(() => {
  reject(new Error('Image load timeout'));
}, 10000);

1. Input Validation: Validate all inputs at entry points
2. Output Encoding: Encode all dynamic content
3. Error Handling: Implement comprehensive error boundaries
4. Resource Limits: Set appropriate limits for all resources
5. Regular Audits: Conduct periodic security reviews

1. HTTPS Required: Serve over HTTPS in production
2. CSP Headers: Implement Content Security Policy
3. HSTS: Use HTTP Strict Transport Security
4. Security Headers: Add appropriate security headers

1. Browser Updates: Encourage users to update browsers
2. Local Storage: Warn about private browsing limitations
3. File Sources: Advise caution with uploaded files
4. Data Backup: Recommend backing up important projects

• All inputs validated and sanitized
• File upload restrictions implemented
• XSS protection verified
• Error handling comprehensive
• Memory limits enforced
• Security headers configured
• HTTPS enabled
• CSP implemented

• Performance monitoring active
• Error logging functional
• Storage quotas enforced
• Input validation working
• File validation operational
• Memory cleanup active

• Security audit (quarterly)
• Dependency review (if any added)
• Browser compatibility testing
• Performance monitoring review
• Error log analysis
• User feedback review

1. XSS Attempt: Malicious script injection detected
2. File Upload Attack: Suspicious file upload behavior
3. Resource Exhaustion: Memory or storage abuse
4. Data Corruption: localStorage tampering detected

1. Immediate: Log incident details
2. Assessment: Determine impact and scope
3. Containment: Implement temporary mitigations
4. Recovery: Restore normal operations
5. Review: Analyze and improve security measures

• Console Logging: Detailed error information
• User Notifications: Appropriate user feedback
• Performance Metrics: Resource usage tracking
• Security Events: Validation failures and attacks

1. Clear Storage: Reset localStorage if corrupted
2. Refresh Application: Reload for clean state
3. Browser Reset: Clear cache and cookies
4. Fallback Mode: Graceful degradation if needed

• OWASP Top 10: Protection against common vulnerabilities
• Client-Side Security: Best practices for browser applications
• Data Protection: Secure handling of user data
• Privacy: No external data transmission

• Static Analysis: Regular code review for security issues
• Secure Coding: Following secure development practices
• Vulnerability Management: Prompt addressing of security issues
• Documentation: Comprehensive security documentation

This security documentation should be reviewed regularly and updated as new features are added or security threats evolve.