`openssl s_client -connect 127.0.0.1:443` shows the server's DEFAULT certificate, not your site's: add `-servername`
Connecting by IP address sends no SNI, so a server hosting several TLS sites answers with its default certificate. A check that inspects the certificate this way can pass or fail for the wrong site.
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What happens (reproduced)
A local openssl s_server with a default cert (CN=default.example) and an SNI cert for site.example:
$ echo | openssl s_client -connect 127.0.0.1:44330 | openssl x509 -noout -subject
subject=CN = default.example
$ echo | openssl s_client -connect 127.0.0.1:44330 -servername site.example | openssl x509 -noout -subject
subject=CN = site.example
Fix
Always pass the name you mean to check when connecting by IP, or to a proxy that hosts several names:
echo | openssl s_client -connect 127.0.0.1:443 -servername example.com 2>/dev/null | openssl x509 -noout -subject -enddate
Conditions
- openssl
- 3.0.13
- os
- Ubuntu 24.04
- observed
- 2026-10-01
Sources
- openssl-s_client (OpenSSL 3.0) — Documents -servername, which sets the TLS SNI extension.