ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY

Enterno.io Editorial Team

By Anatoly Oshmanovsky · Updated Apr 18, 2026

Key idea:

ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY — Chrome refused an HTTP/2 connection because the TLS setup does not meet RFC 7540 requirements: TLS 1.2 minimum, AEAD cipher (GCM, CCM, ChaCha20-Poly1305), ECDHE key exchange. Legacy ciphers (RC4, AES-CBC, 3DES) are forbidden in HTTP/2. Fix: nginx modern ssl_ciphers.

Below: causes, fixes, FAQ.

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Common Causes

TLS 1.1 or lower used with HTTP/2
AES-CBC ciphers (non-AEAD) — forbidden for HTTP/2
No ECDHE ciphers — only RSA key exchange
Blocked cipher list RFC 7540 (long list)
nginx older than 1.13 with legacy cipher defaults

Step-by-Step Fix

nginx modern: ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;
TLS 1.3 cipher suites are HTTP/2-compliant automatically
ssl_prefer_server_ciphers on; + modern config
Enterno SSL Checker shows the cipher list
Or temporarily disable HTTP/2: listen 443 ssl; without http2

Check SSL Certificate →

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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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.

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

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TLS Analysis

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

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DV vs OV vs EV Certificates

DV (Domain Validation)

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Common Mistakes

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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

Why strict HTTP/2 cipher requirements?

RFC 7540 prohibits vulnerable ciphers at the protocol level. Even if TLS accepted the cipher, HTTP/2 rejects it for defence-in-depth.

Does HTTP/3 have the same requirements?

Similar, through QUIC. TLS 1.3 only for QUIC.

Backwards compatibility?

HTTP/1.1 fallback works for old clients. But HTTP/2 — strict cipher requirements.

Mozilla SSL Config Generator?

Use for correct config: ssl-config.mozilla.org. Pick Modern or Intermediate.