HTTP 526 – Invalid SSL Certificate
(Cloudflare) The origin server's SSL certificate is invalid, expired, or does not match, and strict SSL validation is enabled.
Common use case
A frequent cause is a certificate that quietly expired on the origin server while Cloudflare's Full (Strict) SSL mode was still enforcing validation.
History
A Cloudflare-specific extension.
Did you know?
It is one of the most common causes of unexpected outages for sites using automated certificate renewal, since a single failed renewal job on the origin can trigger this for every visitor.