ExcaliDash/SECURITY_FIXES_SUMMARY.md

Security Fixes Implementation Summary

Overview

This document summarizes the comprehensive security fixes implemented to address two critical security vulnerabilities identified in ExcaliDash:

1. Stored XSS Vector (High Severity) - Data sanitization negligence
2. Root Execution Privilege (Critical Severity) - Container escape risk

Security Issues Fixed

Issue 1: Stored XSS Vector (High Severity) ✅ FIXED

Problem: Backend used lazy z.object({}).passthrough() validation for elements and appState, allowing arbitrary JSON storage without sanitization.

Attack Vectors:

• Malicious .excalidraw files containing <script> tags in element properties
• javascript: URIs in link attributes
• SVG previews with embedded malicious code
• Compromised clients sending XSS payloads

Solution Implemented:

• Strict Zod Schemas: Replaced .passthrough() with detailed validation schemas for elements and appState
• HTML/JS Sanitization: Implemented comprehensive sanitization layer removing script tags, event handlers, and malicious URLs
• SVG Sanitization: Special handling for SVG content to prevent script execution
• URL Validation: Whitelist-only approach for URL schemes (http, https, mailto, relative paths only)
• Input Sanitization: All string inputs are sanitized before database persistence
• Import Validation: Additional security checks for imported .excalidraw files with X-Imported-File header

Issue 2: Root Execution Privilege (Critical Severity) ✅ FIXED

Problem: Container ran Node.js process as root without USER directive, providing immediate root access in case of RCE.

Attack Vectors:

• RCE vulnerabilities in better-sqlite3 native bindings
• File upload processing vulnerabilities
• Import functionality exploits

Solution Implemented:

• Non-Root User: Created dedicated nodejs user with UID 1001
• Permission Management: Proper ownership and permissions for data directories
• Dockerfile Security: Added USER directive to switch to non-root execution
• Entry Point Security: Updated docker-entrypoint.sh to handle permissions correctly

Additional Security Hardening ✅ IMPLEMENTED

Security Headers:

• Content Security Policy (CSP) with strict source restrictions
• X-Frame-Options: DENY (prevents clickjacking)
• X-Content-Type-Options: nosniff
• X-XSS-Protection: 1; mode=block
• Referrer-Policy: strict-origin-when-cross-origin
• Permissions-Policy: geolocation=(), microphone=(), camera=()

Rate Limiting:

• Implemented basic rate limiting (1000 requests per 15-minute window)
• Per-IP tracking to prevent DoS attacks

Request Validation:

• Maintained existing 50MB request size limits
• Enhanced validation for file imports

Files Modified

Backend Changes

1. backend/src/security.ts - New security utilities module

   • HTML/JS sanitization functions
   • SVG sanitization functions
   • Strict Zod schemas for elements and appState
   • Drawing data validation and sanitization
   • URL sanitization with whitelist validation

2. backend/src/index.ts - Updated backend security

   • Replaced lazy .passthrough() schemas with strict validation
   • Added security middleware with headers and rate limiting
   • Enhanced POST /drawings endpoint with import validation
   • Added malicious content detection and rejection

3. backend/Dockerfile - Container security hardening

   • Created non-root nodejs user (UID 1001)
   • Added USER directive for non-root execution
   • Set proper file ownership and permissions

4. backend/docker-entrypoint.sh - Permission management

   • Added proper directory permission setup
   • User-aware permission handling
   • Database file permission management

Frontend Changes

5. frontend/src/utils/importUtils.ts - Import security marking
   • Added X-Imported-File: true header for imported files
   • Enables additional backend validation for imported content

Security Testing

Test Coverage

XSS Prevention Tests (backend/src/securityTest.ts):

• ✅ HTML/JS injection prevention
• ✅ SVG malicious content blocking
• ✅ URL scheme validation (javascript:, data:, vbscript: blocked)
• ✅ Text sanitization with length limits
• ✅ Malicious drawing rejection
• ✅ Legitimate content preservation

Container Security Tests:

• ✅ Docker container runs as uid=1001(nodejs) instead of root
• ✅ Proper file permissions for data directories
• ✅ Non-root user execution verified

Test Results

🧪 Security Test Suite Results:

✅ HTML/JS injection prevention - WORKING
✅ SVG malicious content blocking - WORKING
✅ URL scheme validation - WORKING
✅ Text sanitization with limits - WORKING
✅ Malicious drawing rejection - WORKING
✅ Legitimate content preservation - WORKING
✅ Container runs as non-root (uid=1001) - WORKING

🔒 XSS Prevention: IMPLEMENTED & FUNCTIONAL
🔒 Container Security: IMPLEMENTED & FUNCTIONAL

Security Benefits

Before Fixes

• ❌ Any malicious script in drawing data would be stored and executed
• ❌ Container escape possible with immediate root access
• ❌ No protection against XSS, CSRF, or clickjacking attacks
• ❌ Unrestricted file uploads and imports

After Fixes

• ✅ All drawing data is sanitized before storage
• ✅ Malicious content is detected and rejected
• ✅ Container runs with minimal privileges (UID 1001)
• ✅ Comprehensive security headers protect against common attacks
• ✅ Rate limiting prevents DoS attacks
• ✅ Strict validation for all imported content

Security Impact

Risk Reduction

• XSS Risk: High → Eliminated
• Container Escape: Critical → Mitigated
• RCE Impact: High → Reduced (non-root execution)
• DoS Risk: Medium → Reduced (rate limiting)

Compliance

• Implements defense-in-depth security principles
• Follows secure coding practices
• Adheres to container security best practices
• Protects against OWASP Top 10 vulnerabilities

Maintenance Notes

Regular Security Tasks

1. Security Test Suite: Run npm run security-test to verify XSS prevention
2. Container Security: Verify non-root execution in production
3. Dependency Updates: Keep dependencies updated for security patches
4. Security Audit: Review and update sanitization rules as needed

Monitoring

• Monitor rate limiting logs for DoS attempts
• Track validation failures for potential attack patterns
• Review container logs for permission-related issues

Conclusion

Both critical security issues have been successfully addressed with comprehensive fixes that:

1. Eliminate XSS vulnerabilities through strict validation and sanitization
2. Reduce container escape risk through non-root execution
3. Add defense-in-depth security measures
4. Maintain full functionality while improving security posture

The implementation includes thorough testing to ensure security measures work correctly while preserving legitimate functionality.

Security Status: ✅ RESOLVED