Replace the certificate that uses a broken hash

Why it matters

A certificate in the chain is signed with SHA-1 or MD5, hashes that can be forged, so browsers refuse it. It comes from a very old certificate or an old intermediate file.

The fix

1. Find which certificate in the chain uses the weak hash with the command below. It lists each certificate's signature algorithm.
2. If it is your own certificate, re-issue it from your CA, which now signs with SHA-256 or stronger.
3. If it is an intermediate, replace the bundle file with the CA's current chain, or re-issue and use the new fullchain file.
4. Reload the web server and run the command again to confirm.

openssl s_client -connect example.com:443 -servername example.com -showcerts </dev/null 2>/dev/null | awk '/BEGIN CERT/{n++; f="cert" n ".pem"} f{print > f} /END CERT/{f=""}'
for f in cert*.pem; do openssl x509 -in "$f" -noout -subject -text | grep -E "Subject:|Signature Algorithm" | head -2; done

The examples use example.com. Replace it with your own domain.

Read the documentation ↗(opens in a new tab)

Related

• Reported by the certificate chain and expiry check
• Renew the expired TLS certificate
• Fix a certificate that is not valid yet
• Renew the certificate before it expires
• Install a certificate that covers this hostname
• Replace the self-signed certificate with a trusted one
• Use a certificate from a publicly trusted authority
• Serve the full certificate chain
• Replace the expired intermediate certificate
• Re-issue the certificate with a stronger key
• Fix the certificate that browsers reject