- Plesk for Linux
A certificate was installed via Domains > example.com > SSL/TLS Certificates > Upload Certificate
The uploaded certificate is self-signed:
Find the certificate file used by the domain:
# grep -h "SSLCertificateFile|ssl_certificate" /var/www/vhosts/system/example.com/conf/* | tr -d ';' | tr -s' ' | cut -d' ' -f2 | uniq
Run OpenSSL verification:
# openssl verify -verbose /usr/local/psa/var/certificates/cert-Eih3s5
cert-Eih3s5: C = US, ST = Alaska, L = Anchorage, O = Mynewcertificate, CN = www.example.com, emailAddress = firstname.lastname@example.org
error 18 at 0 depth lookup:self signed certificate
A self-signed certificate is being used to secure the connection, and browsers mark self-signed certificates as insecure.
Use Let's Encrypt extension to secure the domain or buy the SSL certificate from trusted issuer and install it instead as described in the article How to install SSL certificate for a domain in Plesk?.