Today I got the SSL certificate mismatch error in my browser (there were no changes in my Netlify account for months). The error went away after a couple of page refreshes, but I was able to capture this on the CLI (can’t reproduce it anymore, sorry):
% openssl s_client -showcerts -servername salt.tips -connect salt.tips:443 </dev/null
CONNECTED(00000003)
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert Global Root CA
verify return:1
depth=1 C = US, O = DigiCert Inc, CN = DigiCert SHA2 Secure Server CA
verify return:1
depth=0 C = US, ST = ca, L = San Francisco, O = "Netlify, Inc", CN = *.netlify.com
verify return:1
---
Certificate chain
0 s:C = US, ST = ca, L = San Francisco, O = "Netlify, Inc", CN = *.netlify.com
i:C = US, O = DigiCert Inc, CN = DigiCert SHA2 Secure Server CA
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
1 s:C = US, O = DigiCert Inc, CN = DigiCert SHA2 Secure Server CA
i:C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert Global Root CA
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
---
Server certificate
subject=C = US, ST = ca, L = San Francisco, O = "Netlify, Inc", CN = *.netlify.com
issuer=C = US, O = DigiCert Inc, CN = DigiCert SHA2 Secure Server CA
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 3316 bytes and written 381 bytes
Verification: OK
---
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---
DONE
So, Netlify briefly served its own SSL certificate for my domain. I also ran the following command (the error was already gone at the time when I did this):
dig +short salt.tips
84.201.139.79
130.193.50.240
Was it a DNS caching issue? A server IP rotation? Not very cool to see my own site blocked by Firefox with a big full-screen SSL warning…
https://www.netlifystatus.com/ is all green.