Summary
Acunetix 360 identified that Expect-CT is not enabled.
Certificate Transparency is a technology that makes impossible (or at least very difficult) for a CA to issue an SSL certificate for a domain without the certificate being visible to the owner of that domain.
Google announced that, starting with April 2018, if it runs into a certificate that is not seen in Certificate Transparency (CT) Log, it will consider that certificate invalid and reject the connection. Thus sites should serve certificate that takes place in CT Logs. While handshaking, sites should serve a valid Signed Certificate Timestamp (SCT) along with the certificate itself.
Expect-CT can also be used for detecting the compatibility of the certificates that are issued before the April 2018 deadline. For instance, a certificate that was signed before April 2018, for 10 years it will be still posing a risk and can be ignored by the certificate transparency policy of the browser. By setting Expect-CT header, you can prevent misissused certificates to be used.
Remediation
Configure your web server to respond with Expect-CT header.
Expect-CT: enforce, max-age=7776000, report-uri="https://ABSOLUTE_REPORT_URL"
Note: We strongly suggest you to use Expect-CT header in report-only mode first. If everything goes well and your certificate is ready, go with the Expect-CT enforce mode. To use report-only mode first, omit enforce flag and see the browser's behavior with your deployed certificate.
Expect-CT: max-age=7776000, report-uri="https://ABSOLUTE_REPORT_URL"