5xx Server errors · Cloudflare (not part of the HTTP standard)
526 Invalid SSL Certificate
With Full (strict) SSL, the origin's certificate couldn't be validated.
Common causes
- An expired, self-signed or wrong-host certificate on the origin.
How to fix it
- Renew or replace the origin certificate.
- Use a Cloudflare Origin CA certificate, which Full (strict) accepts.
Find out the moment your site returns 526
Spot Downtime monitors count this as down and alert you, since visitors see an error. (The public “Is it down?” checker treats 4xx answers from big sites as online, because many refuse automated requests.)