ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY

• 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

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

Check SSL Certificate →

• ERR_SSL_PROTOCOL_ERROR
• NET::ERR_CERT_AUTHORITY_INVALID
• SSL Handshake Failed
• All SSL errors

The SSL error ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY indicates that your server is attempting to establish an HTTP/2 connection using a TLS version or cipher suite that is deemed insecure. To resolve this, ensure that your server supports TLS 1.2 or higher and only uses strong cipher suites, such as AES-GCM. Review your server configuration and update it accordingly to avoid this error.

The ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY error occurs when a client attempts to establish an HTTP/2 connection, but the server's configuration does not meet the security requirements of the protocol. HTTP/2 mandates the use of secure connections via TLS, and as security standards evolve, older versions of TLS (like TLS 1.0 and 1.1) and weak cipher suites are increasingly being deprecated.

Specifically, the HTTP/2 specification requires that a secure connection be established with TLS 1.2 or above. If the server is configured to use an outdated version of TLS or weak ciphers, clients will reject the connection, resulting in this error. This is particularly relevant as browsers and other clients continuously update their security policies, often dropping support for older, less secure protocols.

To ensure compliance, it is important to regularly audit your server's SSL/TLS configuration. You can utilize tools like Qualys SSL Labs' SSL Test, which provides a comprehensive analysis of your SSL configuration and highlights any areas of concern.

Additionally, many compliance frameworks and regulatory bodies (such as PCI DSS) require the use of strong encryption protocols, making it essential for websites handling sensitive information to adhere to these standards.

To resolve the ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY error, follow these steps to ensure your server is configured correctly:

1. Check Your TLS Version: Ensure that your server supports TLS 1.2 or higher. You can check the supported protocols using the following command:

openssl s_client -connect yourdomain.com:443 -tls1_2

If you receive a successful connection response, your server supports TLS 1.2. If not, you will need to update your server configuration.

1. Update Cipher Suites: Review the cipher suites enabled on your server. You should disable weak ciphers and only allow strong ciphers. For example, on an Nginx server, you can specify supported ciphers in your configuration file:

ssl_ciphers 'ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256';

This configuration enforces the use of secure ciphers for TLS connections. Make sure to restart the server after making changes.

1. Enable HTTP/2: If your server is not already configured to support HTTP/2, you can enable it by adding the following directive to your Nginx configuration:

listen 443 ssl http2;

Ensure that this line is present in your server block configuration to allow HTTP/2 connections over SSL.

1. Test Your Configuration: After making the necessary changes, test your server configuration again using the same SSL testing tool to ensure that it meets the required standards for HTTP/2.

By following these steps, you can mitigate the risk of encountering the ERR_HTTP2_INADEQUATE_TRANSPORT_SECURITY error and ensure that your server is compliant with modern security practices.