Understanding Cloudflare SSL/TLS Modes

Cloudflare provides multiple SSL/TLS modes to meet various security and performance requirements, with most features available at no cost. These SSL/TLS modes define the encryption methods used between browsers to Cloudflare and Cloudflare to origin servers.

Introduction to SSL/TLS Modes

1. Automatic SSL/TLS (Default Mode)

   • This is Cloudflare’s default setting, using SSL/TLS Recommender to automatically select the most secure mode
   • It crawls the origin server using Cloudflare-SSLDetector and evaluates content similarity to ensure optimal configuration

2. Custom SSL/TLS

   • Allows users to manually select specific SSL modes to accommodate different origin server configurations

   • Submodes include:

     • Off: No encryption; connections from browser to Cloudflare and Cloudflare to origin server are unencrypted HTTP. This mode provides no security and is only suitable for testing or non-sensitive environments.
     • Flexible: HTTPS encryption between browser and Cloudflare, but unencrypted connection to the origin server. Common when origin servers don’t support TLS, though Cloudflare recommends upgrading origin server configuration when possible.
     • Full: Cloudflare matches the browser’s protocol; uses HTTP to origin server if browser uses HTTP, and HTTPS if browser uses HTTPS, without validating the origin’s certificate. Suitable for origin servers using self-signed or invalid certificates.
     • Full (strict): Similar to Full mode but adds origin certificate validation; certificates must be issued by a public CA (like Let’s Encrypt) or Cloudflare Origin CA. Provides enhanced security for scenarios requiring strict validation.
     • SSL-Only Origin Pull: Cloudflare always uses HTTPS to connect to origin server regardless of browser protocol, and validates certificates. Ensures consistent encryption and validation, ideal for high-security environments.

Cloudflare documentation explicitly recommends using Full or Full (strict) modes to prevent malicious connections and enhance security, especially when handling sensitive data.

SSL/TLS Mode Comparison and Recommendations

To help users choose the appropriate mode, here’s a comparison based on security, performance, and compatibility:

• Security: Strict and Full (strict) modes provide maximum security by ensuring encrypted and validated connections between Cloudflare and origin servers. Flexible mode only encrypts browser-to-Cloudflare connections, leaving origin connections unencrypted. Off mode provides no encryption, offering minimal security.
• Performance: Modes without origin server encryption (like Flexible and Off) may offer slightly better performance by reducing encryption overhead. However, performance differences are typically negligible, especially on modern hardware.
• Compatibility: Flexible or Full modes may be more suitable if origin servers don’t support TLS or use self-signed certificates. Conversely, Full (strict) or Strict modes are recommended when origin servers support TLS with valid certificates, ensuring maximum security.

Cloudflare strongly recommends using Full or Full (strict) modes to prevent malicious connections and enhance security, particularly when handling sensitive data.

Implementation and Best Practices

To configure SSL/TLS modes in Cloudflare, follow these steps:

1. Log into the Cloudflare dashboard
2. Select your domain
3. Navigate to the “SSL/TLS” tab
4. Configure SSL/TLS mode under “Overview”

Best Practices include:

• End-to-End HTTPS: Ensure encrypted connections from browser to Cloudflare and Cloudflare to origin server whenever possible for end-to-end security
• Valid Certificates: For modes requiring certificate validation (like Full (strict) and Strict), ensure origin servers have valid certificates from trusted CAs or use Cloudflare Origin CA
• Monitoring and Updates: Regularly check for security updates and adjust SSL configurations as needed. Monitor TLS protocol version updates (like TLS 1.3) and ensure adherence to latest security practices

Conclusion

Understanding and properly configuring SSL/TLS modes is crucial for protecting web traffic, especially when using CDNs like Cloudflare. By selecting appropriate modes based on origin server capabilities and security requirements, you can ensure secure user experiences while balancing performance and compatibility. Choose suitable SSL/TLS modes for your website and regularly review and update configurations to maintain security.

References

• Cloudflare SSL/TLS Modes