CloudFlare allows traffic for the default cPanel ports, 2082 (HTTP) and 2083 (HTTPS).
To access your cPanel with CloudFlare enabled, try any of the following:
- yourdomain:2083/ (over SSL, so requires paid plan)
- yourdomain.com/cpanel (often a redirect to one of the above)
- cpanel.yourdomain.com (if you've set up that DNS record)
If you have problems with cPanel behind CloudFlare, review "Cookie IP Validation" settings.