PKI & Certificate Troubleshooting

$ openssl s_client -connect payments.acme-corp.com:443 -brief CONNECTION ESTABLISHED Protocol version: TLSv1.3 Cipher suite: TLS_AES_256_GCM_SHA384 Peer certificate: CN=payments.acme-corp.com Hash used: SHA256 Signature type: RSA-PSS Verification: FAILED depth=0 CN=payments.acme-corp.com verify error:num=10:certificate has expired notAfter=Jun 1 23:59:59 2026 GMT Certificate details: Subject: CN=payments.acme-corp.com Issuer: CN=DigiCert TLS RSA SHA256 2020 CA1 notBefore=Jun 2 00:00:00 2025 GMT notAfter =Jun 1 23:59:59 2026 GMT Browser error (Chrome 125): NET::ERR_CERT_DATE_INVALID Your connection is not private. This certificate expired 26 days ago (Jun 1, 2026).

$ openssl verify -CApath /etc/ssl/certs internal-tool.acme.local.pem internal-tool.acme.local.pem: CN=internal-tool.acme.local error 19 at 1 depth lookup: self signed certificate in certificate chain error internal-tool.acme.local.pem: verification failed Certificate chain received: depth=0 CN=internal-tool.acme.local notBefore=Jan 15 00:00:00 2026 GMT notAfter =Jan 15 23:59:59 2027 GMT (valid for another 202 days) depth=1 CN=Acme Internal CA unable to get local issuer certificate Issuer NOT found in system trust store (/etc/ssl/certs) Note: The server sends a leaf + intermediate. The root "CN=Acme Internal CA" is a private/corporate CA not distributed to this workstation — it is unknown to the OS trust store. Dates and chain structure are valid; the CA itself is the problem.

Browser: Chrome 125 — https://mail.acme-corp.com NET::ERR_CERT_COMMON_NAME_INVALID Your connection is not private. Certificate presented by server: Subject CN : www.acme-corp.com X509v3 Subject Alternative Names: DNS:www.acme-corp.com DNS:acme-corp.com Requested hostname : mail.acme-corp.com mail.acme-corp.com is NOT listed in the certificate SAN. Certificate validity: notBefore: Mar 1 00:00:00 2026 GMT notAfter : Mar 1 23:59:59 2027 GMT (valid, 247 days remaining) Chain : OK (DigiCert root trusted by OS) OCSP : good (not revoked)

$ openssl s_client -connect vpn.acme-corp.com:443 -status 2>&1 | head -40 OCSP response: OCSP Response Status: revoked This Update: Jun 20 14:00:00 2026 GMT Revocation Time: Jun 19 09:12:44 2026 GMT Revocation Reason: keyCompromise (1) Certificate details: Subject : CN=vpn.acme-corp.com Issuer : CN=DigiCert TLS RSA SHA256 2020 CA1 notBefore: Jan 10 00:00:00 2026 GMT notAfter : Jan 10 23:59:59 2027 GMT (dates valid — 197 days remaining) Chain : OK (trusted DigiCert root) CN/SAN : vpn.acme-corp.com matches CRL check (http://crl3.digicert.com/sha2-tlsrsa2020ca1-2.crl): Serial 0A:E3:9F:11:7C:44:DE:B9:FF:02:87:1A:54 Status: REVOKED — listed on CRL issued Jun 20 14:00:00 2026 GMT

$ openssl s_client -connect api.acme-corp.com:443 depth=0 CN=api.acme-corp.com verify error:num=20:unable to get local issuer certificate verify error:num=21:unable to verify the first certificate Verify return code: 21 (unable to verify the first certificate) Certificate chain: 0 s:CN=api.acme-corp.com i:CN=DigiCert TLS RSA SHA256 2020 CA1 --- chain stops here (only 1 certificate sent by server) --- The server did NOT send the intermediate certificate (CN=DigiCert TLS RSA SHA256 2020 CA1). Root CA "DigiCert Global Root CA" IS trusted by this system (present in /etc/ssl/certs/DigiCert_Global_Root_CA.pem) — the root is NOT the problem; the intermediate is simply absent. Note: Chrome passes (cached the intermediate from a prior visit). curl and openssl fail because they do not use the browser cache.

$ openssl x509 -text -noout -in legacy.acme-corp.com.pem Certificate: Data: Version: 3 (0x2) Serial Number: 4a:f8:11:cc:b2:3d:09:77 Signature Algorithm: sha1WithRSAEncryption Issuer: CN=VeriSign Class 3 Secure Server CA - G3 Validity Not Before: May 14 00:00:00 2024 GMT Not After : May 13 23:59:59 2026 GMT (valid) Subject: CN=legacy.acme-corp.com X509v3 Subject Alternative Names: DNS:legacy.acme-corp.com X509v3 Extended Key Usage: TLS Web Server Authentication Signature Algorithm: sha1WithRSAEncryption Browser warning (Chrome 125): NET::ERR_CERT_WEAK_SIGNATURE_ALGORITHM This certificate uses a SHA-1 signature, which is considered obsolete cryptography and is no longer trusted.

$ openssl s_client -connect newsite.acme-corp.com:443 -brief CONNECTION ESTABLISHED Protocol version: TLSv1.3 Cipher suite: TLS_AES_128_GCM_SHA256 Peer certificate: CN=newsite.acme-corp.com Verification: FAILED depth=0 CN=newsite.acme-corp.com verify error:num=9:certificate is not yet valid notBefore=Jul 5 00:00:00 2026 GMT Certificate details: Subject: CN=newsite.acme-corp.com Issuer: CN=DigiCert TLS RSA SHA256 2020 CA1 notBefore=Jul 5 00:00:00 2026 GMT <-- 8 days in the FUTURE notAfter =Jul 5 23:59:59 2027 GMT Chain : OK (trusted root) SAN : newsite.acme-corp.com matches OCSP : good System clock on server: Jun 27 08:44:13 UTC 2026 Certificate valid-from: Jul 05 00:00:00 UTC 2026

$ openssl s_client -connect app-gw.acme-corp.com:443 CONNECTED(00000003) depth=0 CN=app-gw.acme-corp.com verify error:num=26:unsupported certificate purpose $ openssl x509 -text -noout -in app-gw.pem | grep -A4 "Extended Key" X509v3 Extended Key Usage: TLS Web Client Authentication Expected for a TLS server: TLS Web Server Authentication <-- NOT present Certificate details: Subject : CN=app-gw.acme-corp.com SAN : DNS:app-gw.acme-corp.com matches Validity: notAfter=Dec 31 2026 (valid) Chain : OK (trusted root) OCSP : good Browser error (Firefox 127): SSL_ERROR_BAD_CERT_DOMAIN The certificate is not valid for this server because it was issued for client authentication, not server authentication.