ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY

• Old nginx/Apache with default 1024-bit DH params
• Unused ssl_dhparam — OpenSSL/Java default 1024-bit
• Cipher list contains DHE-* (no EC)
• Legacy Java server with DH 512
• OpenSSL < 1.0.2 with weak defaults

1. Generate 2048-bit DH: openssl dhparam -out dhparam.pem 2048 (5-10 minutes)
2. nginx: ssl_dhparam /etc/ssl/dhparam.pem;
3. Prefer ECDHE: ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
4. Or drop DHE entirely (ECDHE only)
5. Enterno SSL for DH audit

Check SSL Certificate →

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

The ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY error occurs when a server uses a weak ephemeral Diffie-Hellman (DH) key for SSL/TLS connections, making it vulnerable to attacks like Logjam. To fix this, ensure your server is configured with strong DH parameters (2048 bits or higher) and update your web server software to the latest version. This enhances security and resolves compatibility issues with modern browsers.

The ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY error is a result of using weak or outdated Diffie-Hellman parameters in SSL/TLS configurations. When a client attempts to establish a secure connection with a server that uses a DH key size less than 1024 bits, modern browsers like Chrome and Firefox will reject the connection due to security concerns.

Specifically, the Logjam attack exploits the use of weak DH parameters, allowing an attacker to downgrade the security of the connection. This vulnerability is particularly concerning for web applications handling sensitive data. The Internet Engineering Task Force (IETF) recommends using at least 2048-bit DH parameters to prevent such attacks.

To identify if your server is susceptible to this issue, you can use tools like SSL Labs' SSL Test or OpenSSL commands to inspect your server's SSL/TLS configuration. For example, you can run the following command to check the DH parameters:

openssl s_client -connect yourdomain.com:443 -cipher 'EDH' -msg

If the output indicates a weak DH key size, it is imperative to take corrective measures.

To resolve the ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY error, follow these steps:

1. Update Your Web Server Software: Ensure that your web server (e.g., Apache, Nginx) is up to date. This helps in applying the latest security patches and improvements.
2. Generate Strong DH Parameters: Create a new set of strong DH parameters. For example, to generate a 2048-bit DH parameter file, use the following command:

openssl dhparam -out /etc/ssl/certs/dhparam.pem 2048

1. Configure Your Web Server: Modify your web server configuration to use the newly generated DH parameters. For example, in Nginx, you would add the following lines to your server block:

ssl_dhparam /etc/ssl/certs/dhparam.pem;

1. Verify Your Configuration: Restart your web server to apply the changes. Use the following commands based on your server type:

# For Apache: sudo systemctl restart apache2
# For Nginx: sudo systemctl restart nginx

1. Test Your SSL Configuration: After restarting, use SSL Labs' SSL Test again to confirm that the weak DH parameters are no longer present. Look for the DH key size in the results to ensure it meets the recommended standards.

By following these steps, you can effectively resolve the ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY error and enhance the security of your server's SSL/TLS implementation.