CVSS Vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
The web server is badly configured regarding revoked certificates. Certificate Revocation Lists (CRLs) and the Online Certificate Status Protocol (OCSP) make sure, that users can verify the integrity of a server certificate. If your certificate is compromised, these techniques allow you respectively your certificate authority (CA) to revoke the compromised certificate. Therefore you can issue a new (valid) certificate and the compromised certificate (used by an attacker) will produce warnings when a user accesses their website.
OCSP is the newer method to revoke certificates, as it allows certificate authorities to revoke certificates much faster without the need to update complete revocation lists potentially containing thousands of certificates
Use one of the following guides to make sure that your certificates can be revoked properly:
Unfortunately, you cannot enable OCSP solely on your own. Your certificate authority needs to operate the OCSP server and store the certificate information there. If your CA does not offer OCSP, think of switching to a CA that supports this feature. If your CA supports OCSP, follow these guides to create a certificate with OCSP enabled.
OCSP stapling is an addition to OSCP, where the web server retrieves the OCSP answer from the OCSP server which contains a signed timestamp. This answer is sent to the client on the original request. Therefore the client does not need so sent an additional request to the OCSP server. This increases the privacy of the users as the CA does not get requests of your users which are accessing your web application.
With Let's Encrypt it is very easy to enable OCSP stapling. When creating a new certificate just add the --staple-ocsp flag. If your certificates are already generated by Let's Encrypt, just run the same command and choose "Attempt to reinstall this existing certificate" as the first option. This will reuse your certificate and just enable OCSP stapling.
certbot run -d [DOMAIN] --staple-ocsp --hsts
On Apache you need to get the full certificate chain from your certificate authority and store them in the file/etc/ssl/ca-certs.pem. Then update your SSL configuration to include theSSLStaplingCache,SSLCACertificateFileandSSLUseStapling directives:
Header always set Strict-Transport-Security "max-age=31536000"
On Nginx you need to get the full certificate chain from your certificate authority and store them in the file /etc/ssl/ca-certs.pem. Then update your SSL configuration to include the ssl_stapling, ssl_stapling_verify and ssl_trusted_certificate directives:
add_header Strict-Transport-Security "max-age=63072000; includeSubdomains; ";
index index.html index.htm;