HomeBrandsCloudflareEdge Networkcf-520
C
cf-520
Moderate
Cloudflare · Edge Network
Cloudflare error 520: Unknown origin error.
Quick Answer
Error code CF-520 on your Cloudflare Edge Network means: Cloudflare error 520: Unknown origin error.. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
CF-BUSINESSCF-DNS-PROXYCF-ENTERPRISECF-FREECF-PAGESCF-PROCF-TUNNELCF-WORKERSCF-ZT
Likely Causes
  1. Cloudflare 520 indicates an origin dependency failure: origin returned an unexpected/empty response to Cloudflare.
  2. Origin service health, firewall policy, or upstream network path is degrading edge-to-origin reliability.
  3. TLS/certificate, DNS, or timeout settings between Cloudflare and origin are misaligned.
How to Fix It
1
Correlate Cloudflare 520 timestamp with origin server logs and health metrics.
2
Allow Cloudflare IP ranges at firewall/WAF and verify no upstream deny rules apply.
3
Validate origin DNS target, service listener, and certificate chain requirements.
4
Tune origin timeouts/capacity for slow endpoints or burst traffic conditions.
5
Re-test until Cloudflare 520 no longer appears for affected hostname/path.
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Related Error Codes
CF-1000CF-1001CF-1002CF-1003CF-1004
Video Guides
Loading video guides…
Search more on YouTube →