The driver supports SSL connections to MongoDB servers using the underlying support for SSL provided by the .NET Framework. The driver takes a Network Stream and wraps it with an SslStream. You can configure the use of SSL with the connection string or with MongoClientSettings.

Connection String

The connection string provides 2 options:

  1. ?ssl=true|false You can turn on SSL using this option, or explicitly turn it off. The default is false.
  2. ?sslVerifyCertificate=true|false You can turn off automatic certificate verification using this option. The default is true.
    This option should not be set to false in production. It is important that the server certificate is properly validated.


MongoClientSettings provides a much fuller and robust solution for configuring SSL. It contains the SslSettings property which allows the setting of various values. Each of these values will map very strongly to their counterpart in the SslStream constructor and the AuthenticateAsClient method. For example, to authenticate with a client certificate called “client.pfx”:

var cert = new X509Certificate2("client.pfx", "mySuperSecretPassword");

var settings = new MongoClientSettings
    SslSettings = new SslSettings
        ClientCertificates = new[] { cert },
    UseSsl = true

It is imperative that when loading a certificate with a password, the PrivateKey property not be null. If the property is null, it means that your certificate does not contain the private key and will not be passed to the server.

Certificate Revocation Checking

Default behavior

The .NET Driver now disables certificate revocation checking by default, setting CheckCertificateRevocation in SslSettings to false by default. This correlates to .NET’s defaults for SslStream (see .NET Framework documentation here and .NET Standard documentation here). Applications relying on the intermediate default of true (introduced in beta driver releases 2.11.0-beta1 and 2.11.0-beta2) must explicitly set CheckCertificateRevocation to true in SslSettings to enable certificate revocation checking. Alternatively, applications may also set tlsDisableCertificateRevocationCheck=false in their connection string. See tlsDisableCertificateRevocationCheck for more information.

Prior to v2.7.0, the driver also enabled certificate revocation checking by default.


The URI option, tlsDisableCertificateRevocationCheck controls whether or not to disable certificate revocation checking during a TLS handshake. Setting tlsDisableCertificateRevocationCheck=true is equivalent to setting CheckCertificateRevocation in SslSettings to false.



Due to limitations in .NET, the driver currently only supports OCSP (Online Certificate Status Protocol) stapling on .NET Core ≥2.x on macOS.

On Windows, when a server has a Must-Staple certificate and does not staple, by default, the driver will continue to connect as long as the OCSP responder is still available and reports that the server’s certificate is valid. This behavior differs from the mongo shell and from the MongoDB Python and Go drivers, which will fail to connect in when a server has a Must-Staple certificate and does not staple.

Hard-fail vs. soft-fail

On Windows, due .NET’s implementation of TLS, the driver utilizes “hard-fail” behavior in contrast to the “soft-fail” behavior exhibited by the Linux/macOS mongo shell and MongoDB drivers such as Python and Go. This means that in the case that an OCSP responder is unavailable, the driver will fail to connect (i.e. hard-fail) instead of allowing the connection to continue (i.e. soft-fail).

TLS support


OS .NET Version TLS1.1 TLS1.2 SNI CRLs without OCSP
.NET Framework 4.5 Yes Yes Yes Yes
.NET Framework 4.6 Yes Yes Yes Yes
.NET Framework 4.7 Yes Yes Yes Yes
.NET Core 1.0 Yes Yes Yes Yes
.NET Core 1.1 Yes Yes Yes Yes
.NET Core 2.0 Yes Yes Yes Yes
.NET Core 2.1 Yes Yes Yes Yes
.NET Core 1.0 Yes Yes No Yes
.NET Core 1.1 Yes Yes No Yes
.NET Core 2.0 Yes Yes No Yes
.NET Core 2.1 Yes Yes Yes Yes
.NET Core 1.0 Yes Yes No Yes
.NET Core 1.1 Yes Yes No Yes
.NET Core 2.0 Yes Yes Yes No
.NET Core 2.1 Yes Yes Yes No


  • SNI (Server Name Indication) is required for Atlas free tier.
  • .NET Core on macOS will fail to connect if both of the following conditions are met: (1) certificate revocation checking is enabled, and (2) a server’s certificate includes Certificate Revocation List (CRL) Distribution Points but does not include an Online Certificate Status Protocol (OCSP) extension.

    • This is due to a limitation of the Apple Security Framework (see Prior to version 2.0, .NET Core on macOS used OpenSSL, which does support CRLs without OCSP.
    • Connecting to Atlas on macOS with certificate revocation checking enabled will succeed since Atlas certificates include CRL Distribution Points as well as an OCSP extension.

Support for TLS v1.1 and newer

Industry best practices recommend, and some regulations require, the use of TLS 1.1 or newer. No application changes are required for the driver to make use of the newest TLS protocols.