SSLServerHasCertificateAuthority is false but the certificate is signed by a trusted CA

Question

I am enabling TLS/SSL encryption on a remote MongoDB instance (running on Windows Server 2012 R2). On the instance's server, devserver.external, I have created an SSL certificate. The CN on the subject is devserver.external and the issuer is company-issuer. On my computer (the one with which I am connecting to the remote mongo instance, Windows 10) I have company-issuer in my Intermediate Certification Authorities (when viewed through the Windows certificate manager). This is an internal company operated CA that is trusted on all company machines, including the dev server and my machine.

When connecting to mongo, via either mongo on the command line or the Robo3t client, the connection succeeds over SSL but db.serverStatus().security.SSLServerHasCertificateAuthority is false. From the mongo docs:

A boolean that is true when the TLS/SSL certificate specified by net.ssl.PEMKeyPassword is associated with a certificate authority. **false when the TLS/SSL certificate is self-signed.**

So it would seem mongo is interpreting my CA-signed certificate as a self-signed certificate. This is obviously unwanted behaviour.

My mongod.cfg is:

systemLog:
    destination: file
    path: E:\MongoData\Log\mongod.log
storage:
    dbPath: e:\MongoData\DB
setParameter:
    enableLocalhostAuthBypass: false
security:
    authorization: enabled
net:
    ssl:
        mode: requireSSL
        PEMKeyFile: C:\Program Files\MongoDB\Server\3.4\mongodb2.pem

My mongodb2.pem is:

-----BEGIN PRIVATE KEY-----
<base64 encoded private key>
-----END PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
<base64 encoded certificate>
-----END CERTIFICATE-----

I've not included a CA file because as stated in the configuration reference:

Changed in version 3.4: If --sslCAFile is not specified when connecting to an TLS/SSL-enabled server, the system-wide CA certificate store will be used.

My interpretation of this is: As I have not included a net.ssl.CAFile in my mongod.cfg, my mongo server will look to the Windows certificate store for a list of trusted CAs. In which it would find my company-issuer CA, which is the issuer for the certificate in mongodb2.pem.

Answer 1

As MongoDB BOL documentation here to connect to a mongod or mongos instance that requires encrypted communication, start mongo shell with --ssl and include the --sslCAFile to validate the server certificates.

mongo --ssl --host hostname.example.com --sslCAFile /etc/ssl/ca.pem

For example, given an TLS/SSL certificate located at /etc/ssl/mongodb.pem, configure mongod to use TLS/SSL encryption for all connections with the following command:

mongod --sslMode requireSSL --sslPEMKeyFile /etc/ssl/mongodb.pem <additional options>

Set Up mongod and mongos with Certificate Validation

To set up mongod or mongos for TLS/SSL encryption using an TLS/SSL certificate signed by a certificate authority, include the following run-time options during startup:

• net.ssl.mode set to requireSSL. This setting restricts each server to use only TLS/SSL encrypted connections. You can also specify either the value allowSSL or preferSSL to set up the use of mixed TLS/SSL modes on a port. See net.ssl.mode for details.
• PEMKeyfile with the name of the .pem file that contains the signed TLS/SSL certificate and key.
• CAFile with the name of the .pem file that contains the root
  certificate chain from the Certificate Authority.

Note:

1. Specify the file and the file with either the full path name or the relative path name.
2. If the is encrypted, specify the passphrase. See TLS/SSL Certificate Passphrase.

You may also specify these options in the configuration file, as in the following examples:

If using the YAML configuration file format, include the following configuration in the file:

net:
   ssl:
      mode: requireSSL
      PEMKeyFile: /etc/ssl/mongodb.pem
      CAFile: /etc/ssl/ca.pem

Connect to MongoDB Instance that Requires Client Certificates

To connect to a mongod or mongos that requires CA-signed client certificates, start the mongo shell with --ssl, the --host option to specify the host to which to connect, the --sslPEMKeyFile option to specify the signed certificate-key file, and the --sslCAFile to validate the server certificates.

mongo --ssl --host hostname.example.com --sslPEMKeyFile /etc/ssl/client.pem --sslCAFile /etc/ssl/ca.pem