x.509

Client Certificate Requirements

Client certificates must have the following properties:

• A single Certificate Authority (CA) must issue the certificates for both the client and the server.

• Client certificates must contain the following fields:

  keyUsage = digitalSignature
  extendedKeyUsage = clientAuth

• Each unique MongoDB user must have a unique certificate.

• A client x.509 certificate's subject, which contains the Distinguished Name (DN), must differ from the subjects of member x.509 certificates.

  Important

  If a client x.509 certificate's subject matches the O, OU, and DC attributes of the Member x.509 Certificate (or tlsX509ClusterAuthDNOverride, if set) exactly, the client connection is accepted, full permissions are granted, and a warning message appears in the log.

  Only cluster member x509 certificates should use the same O, OU, and DC attribute combinations.

  If the MongoDB deployment has tlsX509ClusterAuthDNOverride set, the client x.509 certificate's subject must not match that value.

  If the MongoDB deployment has tlsX509ClusterAuthDNOverride set, the client x.509 certificate's subject must also differ from that value.

• The x.509 certificate must not be expired.

  mongod / mongos logs a warning on connection if the presented x.509 certificate expires within 30 days of the mongod/mongos host system time.

MongoDB User and $external Database

To authenticate with a client certificate, you must first add the value of the subject from the client certificate as a MongoDB user. Each unique x.509 client certificate corresponds to a single MongoDB user. You cannot use a single client certificate to authenticate more than one MongoDB user.

Add the user in the $external database. The $external database is the Authentication Database for the user.

To use Client Sessions and Causal Consistency Guarantees with $external authentication users (Kerberos, LDAP, or x.509 users), the usernames cannot be greater than 10k bytes.

TLS Connection X509 Certificate Startup Warning

Starting in MongoDB 5.0, mongod and mongos now issue a startup warning when their certificates do not include a Subject Alternative Name attribute.

The following platforms do not support common name validation:

• iOS 13 and higher

• MacOS 10.15 and higher

• Go 1.15 and higher

Clients using these platforms will not authenticate to MongoDB servers which use X.509 certificate whose hostnames are specified by CommonName attributes.

Member Certificate Requirements

Member certificates which you use to verify membership to a sharded cluster or a replica set (net.tls.clusterFile, if specified, and net.tls.certificateKeyFile), must have the following properties:

• A single Certificate Authority (CA) must issue all the x.509 certificates for the members of a sharded cluster or a replica set.

• The Distinguished Name (DN), found in the member certificate's subject, must specify a non-empty value for at least one of the following attributes:

  • the Organization (O)

  • the Organizational Unit (OU)

  • the Domain Component (DC)

• The Organization attributes (O's), the Organizational Unit attributes (OU's), and the Domain Components (DC's) must match those from both the net.tls.clusterFile and net.tls.certificateKeyFile certificates for the other cluster members (or the tlsX509ClusterAuthDNOverride value, if set).

  To match, the certificate must match all specifications of these attributes, even the non-specification of these attributes. The order of the attributes does not matter.

  In the following example, the two DN's contain matching specifications for O, OU as well as the non-specification of the DC attribute.

  CN=host1,OU=Dept1,O=MongoDB,ST=NY,C=US
  C=US, ST=CA, O=MongoDB, OU=Dept1, CN=host2

  However, the following two DN's contain a mismatch for the OU attribute since one contains two OU specifications and the other, only one specification.

  CN=host1,OU=Dept1,OU=Sales,O=MongoDB
  CN=host2,OU=Dept1,O=MongoDB

• In multi-cluster deployments, each cluster must use a different X.509 member certificate. Each certificate must have unique values on the O, OU, and DC Distinguished Name (DN) fields.

  If two clusters have certificates with the same DN values, a compromised server on one cluster can authenticate as a member of the other.

• Either the Common Name (CN) or one of the Subject Alternative Name (SAN) entries must match the server hostname for other cluster members. Starting in MongoDB 4.2, when comparing SANs, MongoDB can compare either DNS names or IP addresses. In previous versions, MongoDB only compares DNS names.

  For example, the certificates for a cluster could have the following subjects:

  subject= CN=<myhostname1>,OU=Dept1,O=MongoDB,ST=NY,C=US
  subject= CN=<myhostname2>,OU=Dept1,O=MongoDB,ST=NY,C=US
  subject= CN=<myhostname3>,OU=Dept1,O=MongoDB,ST=NY,C=US

• If the certificate used as the certificateKeyFile includes extendedKeyUsage, the value must include both clientAuth ("TLS Web Client Authentication") and serverAuth ("TLS Web Server Authentication").

  extendedKeyUsage = clientAuth, serverAuth

• If the certificate used as the clusterFile includes extendedKeyUsage, the value must include clientAuth.

  extendedKeyUsage = clientAuth

• The x.509 certificate must not be expired.

  mongod / mongos logs a warning on connection if the presented x.509 certificate expires within 30 days of the mongod/mongos host system time.

MongoDB Configuration for Membership Authentication

You can use TLS for internal authentication between each member of your replica set (each mongod instance) or sharded cluster (each mongod and mongos instance).

To use TLS for internal authentication, use the following settings:

• security.clusterAuthMode or --clusterAuthMode set to x509

• net.tls.clusterFile or --tlsClusterFile

mongod and mongos instances use their certificate key file to prove their identity to clients, but it can also be used for membership authentication. If you do not specify a cluster file, members use their certificate key files for membership authentication. Specify the certificate key file with net.tls.certificateKeyFile or --tlsCertificateKeyFile.

To use the certificate key file for both client authentication and membership authentication, the certificate must either:

• Omit extendedKeyUsage or

• Specify extendedKeyUsage = serverAuth, clientAuth