SSL Certificate Errors — Troubleshooting
ssl certificate error fix · certificate name mismatch · ssl troubleshooting guide
Fix common SSL errors: name mismatch, untrusted chain, expired cert, mixed content, and SNI issues using online checkers and DNS/WHOIS context.
By DN01 Network Team
TLS errors surface in browsers, API clients, and monitoring probes with different messages for the same root cause. A structured checklist — hostname, dates, chain, protocol — resolves most incidents without guessing.
Start with the SSL Certificate Checker on the exact hostname users type, then cross-check DNS A/AAAA records and WHOIS if the wrong server answers.
Name mismatch (SAN/CN)
Certificate must list every hostname served — www and apex are distinct unless both in SAN.
Legacy CN-only certs fail when clients require SAN — re-issue with complete SAN list.
Multi-tenant servers need correct SNI — wrong virtual host cert produces mismatch on shared IP.
Mixed content and redirects
Active HTTPS with passive HTTP assets triggers browser warnings — use HTTP Header Checker and fix asset URLs.
HTTP→HTTPS redirect loops often involve misconfigured HSTS or proxy headers — verify redirect chain separately.
Frequently asked questions
- Error only from one country?
Check GeoDNS, CDN edge cert, or regional resolver hitting a stale anycast node.
- API clients fail but browser works?
Clients may require TLS 1.2+, specific cipher, or complete chain — compare checker cipher/protocol with client logs.
- Should I disable certificate validation in apps?
Never in production. Fix the chain or trust store instead.