On Wednesday, September 29th 2021 a widely used Certificate Authority from Let’s Encrypt expired and brought the world to its knee. Well, at least my homelab, anyways. The exact message would be something like “The following CA/Certificate entries are expiring: Certificate Authority: Acmecert: O=Let’s Encrypt, CN=Let’s Encrypt Authority R3, C=US”
The fix is quite simple, just visit System >> Cert Manager >> CAs and find the entry “Acmecert: O=Let’s Encrypt, CN=Let’s Encrypt Authority R3, C=US”. You will see a “Valid until” in yellow, with 09/29/2021 as the Ragnarok day. Note also there is a “R3” in the CA name which is different than X3. Just click on Delete (trash bin icon) and confirm click on Ok.
This is safe to do because you have another CA for Let’sEncrypt which contains “R3” in the name. The new R3 will have been issues by Acmecert: O=Internet Security Research Group, CN=ISRG Root X1, C=US
Remember to renew all of your certificates just to be safe.
That is it, have fun!