SSL_ERROR_PROTOCOL_VERSION_ALERT — TLS Version Mismatch

Enterno.io Editorial Team

SSL_ERROR_PROTOCOL_VERSION_ALERT: Causes

By Anatoly Oshmanovsky · Updated Apr 18, 2026

Key idea:

SSL_ERROR_PROTOCOL_VERSION_ALERT — TLS alert 70 (protocol_version). Server does not support the requested TLS version. Typically happens when the browser tries TLS 1.3 but server is stuck on TLS 1.2 (OK) or 1.0/1.1 (fail — browsers disabled them). Alternative: browser offers old TLS, server requires newer.

Below: causes, fixes, FAQ.

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Common Causes

Server stuck on TLS 1.0/1.1 (blocked by Chrome/Firefox since 2020)
OpenSSL < 1.0.2 — no ALPN + TLS 1.2
Legacy nginx (1.13-) — TLS 1.2 only, no 1.3
Downgrade attack prevention: TLS_FALLBACK_SCSV detected
Custom TLS config disabled the requested version

Step-by-Step Fix

Enable TLS 1.2 + 1.3 in nginx: ssl_protocols TLSv1.2 TLSv1.3;
Update OpenSSL to 3.x
Check supported TLS: openssl s_client -connect example.com:443 -tls1_3
Enterno SSL Checker lists all supported TLS versions
See the nginx SSL install guide

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Related SSL Errors

CertificateExpiry, issuer, domains (SAN)

ChainIntermediate and root CA validation

TLS ProtocolTLS version and cipher suite

VulnerabilitiesHeartbleed, POODLE, weak ciphers

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TLS 1.3

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How it works

Enter domain

TLS chain verified

Expiry date & vulnerabilities

What Does the SSL Check Cover?

SSL/TLS is the encryption protocol that protects data between the browser and server. Our tool analyzes the certificate, chain of trust, TLS version, and knownvulnerabilities.

Certificate Details

Issuer, validity period, signature algorithm, covered domains (SAN), and validation type (DV/OV/EV).

Chain of Trust

Full chain verification: from leaf certificate through intermediates to root CA.

TLS Analysis

Protocol version (TLS 1.2/1.3), cipher suites, Perfect Forward Secrecy (PFS) support.

Expiry Alerts

Set up a monitor — get Telegram and email alerts 30/14/7 days before expiration.

DV vs OV vs EV Certificates

DV (Domain Validation)

Confirms domain ownership only
Issued in minutes automatically
Free via Let's Encrypt
Suitable for most websites
Most common certificate type

OV / EV

Organization (OV) or Extended Validation (EV)
Issued in 1-5 business days
Costs $50 to $500/year
For finance, e-commerce, government sites
Increases user trust

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DevOps

SSL certificate monitoring

Security

TLS config audit

SEO

HTTPS as ranking factor

E-commerce

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Common Mistakes

❌

Expired certificateBrowsers block sites with expired SSL. Set up auto-renewal or monitoring.

❌

Incomplete certificate chainWithout intermediate CA, some browsers and bots cannot verify the certificate.

❌

Mixed content on HTTPS siteHTTP resources on an HTTPS page — the browser lock icon disappears, reducing trust.

❌

Using TLS 1.0/1.1Legacy TLS versions have known vulnerabilities. Use TLS 1.2+ or 1.3.

❌

Domain mismatch in certificateThe certificate must cover all site domains, including www and subdomains.

Best Practices

✓

Set up auto-renewalLet's Encrypt + certbot with cron — certificate renews automatically every 60-90 days.

✓

Enable HSTSStrict-Transport-Security header forces browsers to always use HTTPS.

✓

Use TLS 1.3TLS 1.3 is faster (1-RTT handshake) and safer — legacy ciphers removed.

✓

Monitor expiration datesCreate a monitor on Enterno.io — get notified well before expiration.

✓

Verify chain after renewalAfter certificate renewal, confirm that intermediate certificates are installed.

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Research

TLS 1.3 Adoption 2026: Growth Pace

Errors

Frequently Asked Questions

Do Chrome and Firefox block the same?

Yes, since 2020: TLS 1.0 + 1.1 disabled. Safari, Edge followed. TLS 1.2 is the minimum.

How to find out which TLS my server runs?

<a href="/en/ssl">Enterno SSL</a> shows supported versions. Or <code>openssl s_client -connect host:443 -tls1_3</code>.

Worked yesterday, broke today — what?

Usually a browser auto-update. Chrome 84+ (July 2020) enabled TLS 1.0/1.1 block by default.

Is TLS 1.2 safe in 2026?

Yes. TLS 1.3 is better, but 1.2 is secure with proper ciphers. Both are accepted standards.