ADR-0014: Security Headers and Environment-Aware CORS Middleware

ADR-0014: Security Headers and Environment-Aware CORS Middleware

• Status: Accepted
• Date: 2025-08-17
• Deciders: Core Engineering Team
• Issues: #344, #533
• Related: Addresses all 9 security headers identified by nodejsscan

Context

ContextForge needed comprehensive security headers and proper CORS configuration to prevent common web attacks including XSS, clickjacking, MIME sniffing, and cross-origin attacks. Additionally, the nodejsscan static analysis tool identified 9 missing security headers specifically for the Admin UI and static assets.

The previous implementation had:

• Basic CORS middleware with wildcard origins in some configurations
• Limited security headers only in the DocsAuthMiddleware
• No comprehensive security header implementation
• Manual CORS origin configuration without environment awareness
• Admin UI cookie settings without proper security attributes
• No static analysis tool compatibility

Security requirements included:

• Essential security headers for all responses (issue #344)
• Configurable security headers for Admin UI and static assets (issue #533)
• Environment-aware CORS configuration for development vs production
• Secure cookie handling for authentication
• Admin UI compatibility with Content Security Policy
• Static analysis compatibility for nodejsscan and similar tools
• Backward compatibility with existing configurations

Decision

We implemented a comprehensive security middleware solution with the following components:

1. SecurityHeadersMiddleware

Created mcpgateway/middleware/security_headers.py that automatically adds essential security headers to all responses:

# Essential security headers
response.headers["X-Content-Type-Options"] = "nosniff"
response.headers["X-Frame-Options"] = "DENY"
response.headers["X-XSS-Protection"] = "0"  # Modern browsers use CSP
response.headers["X-Download-Options"] = "noopen"  # Prevent IE downloads
response.headers["Referrer-Policy"] = "strict-origin-when-cross-origin"

# Content Security Policy (Admin UI compatible)
csp_directives = [
    "default-src 'self'",
    "script-src 'self' 'unsafe-inline' 'unsafe-eval' https://cdnjs.cloudflare.com https://cdn.tailwindcss.com https://cdn.jsdelivr.net",
    "style-src 'self' 'unsafe-inline' https://cdnjs.cloudflare.com",
    "img-src 'self' data: https:",
    "font-src 'self' data:",
    "connect-src 'self' ws: wss: https:",
    "frame-ancestors 'none'"
]

# HSTS for HTTPS connections
if request.url.scheme == "https" or request.headers.get("X-Forwarded-Proto") == "https":
    response.headers["Strict-Transport-Security"] = "max-age=31536000; includeSubDomains"

# Remove sensitive headers
del response.headers["X-Powered-By"]  # if present
del response.headers["Server"]        # if present

2. Environment-Aware CORS Configuration

Enhanced CORS setup in mcpgateway/main.py with automatic origin configuration:

Development Environment:

• Automatically configures origins for common development ports: localhost:3000, localhost:8080, gateway port
• Includes both localhost and 127.0.0.1 variants
• Allows HTTP origins for development convenience

Production Environment:

• Constructs HTTPS origins from APP_DOMAIN setting
• Creates origins: https://{domain}, https://app.{domain}, https://admin.{domain}
• Enforces HTTPS-only origins
• Never uses wildcard origins

3. Secure Cookie Utilities

Added mcpgateway/utils/security_cookies.py with functions for secure authentication:

def set_auth_cookie(response: Response, token: str, remember_me: bool = False):
    use_secure = (settings.environment == "production") or settings.secure_cookies
    response.set_cookie(
        key="jwt_token",
        value=token,
        max_age=30 * 24 * 3600 if remember_me else 3600,
        httponly=True,      # Prevents JavaScript access
        secure=use_secure,  # HTTPS only in production
        samesite=settings.cookie_samesite,  # CSRF protection
        path="/"
    )

4. Configurable Security Headers

Added comprehensive configuration options to mcpgateway/config.py for all security headers:

# Environment awareness
environment: str = Field(default="development", env="ENVIRONMENT")
app_domain: str = Field(default="localhost", env="APP_DOMAIN")

# Cookie Security
secure_cookies: bool = Field(default=True, env="SECURE_COOKIES")
cookie_samesite: str = Field(default="lax", env="COOKIE_SAMESITE")

# CORS Configuration
cors_allow_credentials: bool = Field(default=True, env="CORS_ALLOW_CREDENTIALS")

# Security Headers Configuration (issue #533)
security_headers_enabled: bool = Field(default=True, env="SECURITY_HEADERS_ENABLED")
x_frame_options: str = Field(default="DENY", env="X_FRAME_OPTIONS")
x_content_type_options_enabled: bool = Field(default=True, env="X_CONTENT_TYPE_OPTIONS_ENABLED")
x_xss_protection_enabled: bool = Field(default=True, env="X_XSS_PROTECTION_ENABLED")
x_download_options_enabled: bool = Field(default=True, env="X_DOWNLOAD_OPTIONS_ENABLED")
hsts_enabled: bool = Field(default=True, env="HSTS_ENABLED")
hsts_max_age: int = Field(default=31536000, env="HSTS_MAX_AGE")
hsts_include_subdomains: bool = Field(default=True, env="HSTS_INCLUDE_SUBDOMAINS")
remove_server_headers: bool = Field(default=True, env="REMOVE_SERVER_HEADERS")

5. Static Analysis Tool Compatibility

Added security meta tags to mcpgateway/templates/admin.html for static analysis tool compatibility:

<!-- Security meta tags for static analysis tools (complement HTTP headers) -->
<meta http-equiv="Content-Security-Policy" content="..." />
<meta http-equiv="X-Frame-Options" content="DENY" />
<meta http-equiv="X-Content-Type-Options" content="nosniff" />
<meta http-equiv="X-XSS-Protection" content="1; mode=block" />
<meta http-equiv="X-Download-Options" content="noopen" />

6. Enhanced Static Analysis

Updated Makefile to scan both static files and templates:

nodejsscan:
    @$(VENV_DIR)/bin/nodejsscan --directory ./mcpgateway/static --directory ./mcpgateway/templates || true

Consequences

✅ Benefits

• Comprehensive Protection: All responses include essential security headers
• Automatic Configuration: CORS origins are automatically configured based on environment
• Admin UI Compatible: CSP allows required CDN resources while maintaining security
• Production Ready: Secure defaults for production deployments
• Development Friendly: Permissive localhost origins for development
• Backward Compatible: Existing configurations continue to work
• Cookie Security: Authentication cookies automatically configured with security flags
• HTTPS Detection: HSTS header added automatically when HTTPS is detected

❌ Trade-offs

• CSP Flexibility: Using 'unsafe-inline' and 'unsafe-eval' for Admin UI compatibility
• CDN Dependencies: CSP allows specific external CDN domains
• Configuration Complexity: More environment variables to configure
• Development Overhead: Additional middleware processing on every request

🔄 Maintenance

• CSP Updates: May need updates if Admin UI adds new external dependencies
• CDN Changes: CSP must be updated if CDN URLs change
• Security Reviews: Periodic review of CSP directives for security improvements
• Browser Updates: Monitor browser CSP implementation changes

Alternatives Considered

Implementation Details

Middleware Order

# Order matters - security headers should be added after CORS
app.add_middleware(CORSMiddleware, ...)      # 1. CORS first
app.add_middleware(SecurityHeadersMiddleware) # 2. Security headers
app.add_middleware(DocsAuthMiddleware)       # 3. Auth protection

Environment Detection

• Uses ENVIRONMENT setting to determine development vs production mode
• Falls back to safe defaults if environment not specified
• Only applies automatic origins when using default configuration

CSP Design Decisions

• 'unsafe-inline': Required for Tailwind CSS inline styles and Alpine.js
• 'unsafe-eval': Required for some JavaScript frameworks used in Admin UI
• Specific CDN domains: Whitelisted known-good CDN sources instead of wildcard
• 'frame-ancestors none': Prevents all framing to prevent clickjacking

iframe Embedding Configuration

By default, iframe embedding is disabled for security via X-Frame-Options: DENY and frame-ancestors 'none'. To enable iframe embedding:

1. Same-domain embedding: Set X_FRAME_OPTIONS=SAMEORIGIN
2. Specific domain embedding: Set X_FRAME_OPTIONS=ALLOW-FROM https://trusted-domain.com
3. Disable frame protection: Set X_FRAME_OPTIONS="ALLOW-ALL" (not recommended)

Note: When changing X-Frame-Options, also consider updating the CSP frame-ancestors directive for comprehensive browser support.

Testing Strategy

Implemented comprehensive test coverage (42 new tests):

• Security headers validation across all endpoints
• CORS behavior testing for allowed and blocked origins
• Environment-aware configuration testing
• Cookie security attributes validation
• Production security posture verification
• CSP directive structure validation
• HSTS behavior testing

Subresource Integrity (SRI) Implementation

Status: ✅ Implemented (Issue #2558)

As part of the security enhancements, Subresource Integrity (SRI) has been implemented for all external CDN resources to cryptographically verify that fetched resources have not been tampered with.

Implementation Overview

1. Hash Generation: scripts/generate-sri-hashes.py generates SHA-384 hashes for all CDN resources
2. Hash Storage: Hashes stored in mcpgateway/sri_hashes.json and loaded via load_sri_hashes() in admin.py
3. Template Integration: All CDN resources in templates include integrity and crossorigin attributes
4. CI Verification: scripts/verify-sri-hashes.py validates hashes match CDN content in CI pipeline

Protected Resources

All 15 external CDN resources are protected with SRI hashes:

• HTMX (1.9.10) - Dynamic interactions
• Alpine.js (3.14.1) - Reactive framework
• Chart.js (4.4.1) - Data visualization
• Marked (11.1.1) - Markdown parser
• DOMPurify (3.0.6) - XSS sanitizer
• CodeMirror (5.65.18) - Code editor (7 files: core, modes, themes)
• Font Awesome (6.4.0) - Icon library

Security Benefits

• CDN Compromise Protection: Hash mismatch blocks execution
• MITM Attack Prevention: Tampered content detected
• Version Drift Detection: CI catches unexpected changes
• Automated Verification: Every CI run validates hashes

Usage

# Generate SRI hashes for all CDN resources
make sri-generate

# Verify hashes match current CDN content
make sri-verify

Updating CDN Libraries

When updating a CDN library version:

1. Update the URL in scripts/cdn_resources.py
2. Run make sri-generate to calculate new hash
3. Update the URL in templates (admin.html, login.html, etc.)
4. Run make sri-verify to confirm hash matches
5. Commit both sri_hashes.json and template changes

Future Enhancements

Potential improvements for future iterations:

• CSP Nonces: Replace 'unsafe-inline' with nonces for dynamic content
• CSP Violation Reporting: Implement CSP violation reporting endpoint
• Per-Route CSP: Different CSP policies for different endpoints
• Security Header Compliance: Monitoring dashboard for header compliance

Status

This security headers and CORS middleware implementation is accepted and implemented as of version 0.5.0, providing comprehensive security coverage while maintaining compatibility with existing functionality.

SRI Implementation: Completed in version 1.0.0 (Issue #2558) - All external CDN resources now protected with SHA-384 integrity hashes.