The DST Root CA X3 certificate expired, leaving many devices on the internet having issues connecting to services and certificates that use this Root CA, including those using Let’s Encrypt certificates.
Some of these problematic devices include Samsung Galaxy phones, iPhones, VDI zero and thin clients, and even Sophos UTM firewalls.
The Problem
Let’s Encrypt originally used the “DST Root CA X3” certificate to issue Let’s Encrypt certificates. However, as time has passed and the service has been used more, they now use “ISRG Root X1” and “ISRG Root X2” as Root CA’s and “Let’s Encrypt R3” as an intermediate certificate.
Older devices may be using the older Root CA which expired today (September 30th, 2021). Please see https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/ for more information.
The Fix
To fix this issue, you need to add the 2 new Root CAs to your computer or device.
Root CA Certificates (PEM format):
Intermediate Certificate (PEM format):
You can download them by clicking the links above or go to https://letsencrypt.org/certificates/ for more information and to download if you don’t trust the above links.
After downloading and adding these Root CAs and the Intermediate CA to your computer or device, you should have the full certificate chain to validate the Let’s Encrypt certificates. You only need to add the two root certificates. The Let’s Encrypt certificates that are used on websites that you visit and that you might have deployed on your servers should now work without any issues.
*Steps to import PEM Certificates
Go to windows search, type “Internet Options”
Go to Contents > Certificates > Trusted Root Certification Authorities > Import > Browse > Select All Files on top of the “Open” and “Cancel” button > Select ISRG Root X1. Do the same steps for ISRG Root X2.
Source: www.stephenwagner.com