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What causes the Error 526 on Cloudflare?

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One of my sites keeps having this happen. Both are on the same server which is confusing me. I figured if it was happening on one, it would happen on the other but this is not the case. It doesn't happen all the time either. It seems to be at random and comes and goes. Anyone know what could be causing this?

This error occurs exclusively when the Cloudflare SSL/TLS encryption mode is set to Full (Strict), which mandates that the connection to the origin be encrypted and the certificate be valid, trusted, and correctly configured. The certification could be expired or untrusted.

Check the DNS. Sometimes that could be viewed as invalid and you have to switch it from DNS online to proxied. This could also be why one works and the other is getting an error. I hope something gets sorted. I know how annoying Cloudflare errors can be!

  • 2 weeks later...

It just means you are triggering for an invalid certificate or it is expired. This can sometimes happen at random and self-correct itself but it is rare. If you recently transferred your DNS to Cloudflare, I have heard of that giving people trouble too.

  • 2 weeks later...

I had this a few times and yes, the certificate is likely being read as invalid. In my case, the first time it was expired and it was an easy fix. The second time, it happened on and off like you mentioned and then stopped after I updated my browser for some reason. Been fine since!

  • 2 weeks later...

As far as I could find, in terms of what causes it - these seem to be the main causes :

  • Expired Certificate: The most frequent cause; the origin's SSL certificate has passed its validity date.

  • Self-Signed Certificate: The origin uses a certificate not issued by a public Certificate Authority (CA), which Cloudflare does not trust in Strict mode.

  • Hostname Mismatch: The certificate is issued for a different domain or subdomain than the one Cloudflare is accessing.

  • Incomplete Certificate Chain: The origin server is missing intermediate certificates required to build a chain of trust to a root CA.

  • Revoked Certificate: The certificate has been revoked by the issuing CA.

I am not seeing any other reasons for it to happen. I have had it a few times and it was down the an expired certificate both times.

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