TLS/SSL and PyMongo#

PyMongo supports connecting to MongoDB over TLS/SSL. This guide covers the configuration options supported by PyMongo. See the server documentation to configure MongoDB.


Industry best practices recommend, and some regulations require, the use of TLS 1.1 or newer. Though no application changes are required for PyMongo to make use of the newest protocols, some operating systems or versions may not provide an OpenSSL version new enough to support them.

Users of macOS older than 10.13 (High Sierra) will need to install Python from, homebrew, macports, or another similar source.

Users of Linux or other non-macOS Unix can check their OpenSSL version like this:

$ openssl version

If the version number is less than 1.0.1 support for TLS 1.1 or newer is not available. Contact your operating system vendor for a solution or upgrade to a newer distribution.

You can check your Python interpreter by installing the requests module and executing the following command:

python -c "import requests; print(requests.get('', verify=False).json()['tls_version'])"

You should see “TLS 1.X” where X is >= 1.

You can read more about TLS versions and their security implications here:

Basic configuration#

In many cases connecting to MongoDB over TLS/SSL requires nothing more than passing tls=True as a keyword argument to MongoClient:

>>> client = pymongo.MongoClient('', tls=True)

Or passing tls=true in the URI:

>>> client = pymongo.MongoClient('mongodb://')

This configures PyMongo to connect to the server using TLS, verify the server’s certificate and verify that the host you are attempting to connect to is listed by that certificate.

Certificate verification policy#

By default, PyMongo is configured to require a certificate from the server when TLS is enabled. This is configurable using the tlsAllowInvalidCertificates option. To disable this requirement pass tlsAllowInvalidCertificates=True as a keyword parameter:

>>> client = pymongo.MongoClient('',
...                              tls=True,
...                              tlsAllowInvalidCertificates=True)

Or, in the URI:

>>> uri = 'mongodb://'
>>> client = pymongo.MongoClient(uri)

Specifying a CA file#

In some cases you may want to configure PyMongo to use a specific set of CA certificates. This is most often the case when you are acting as your own certificate authority rather than using server certificates signed by a well known authority. The tlsCAFile option takes a path to a CA file. It can be passed as a keyword argument:

>>> client = pymongo.MongoClient('',
...                              tls=True,
...                              tlsCAFile='/path/to/ca.pem')

Or, in the URI:

>>> uri = 'mongodb://'
>>> client = pymongo.MongoClient(uri)

Specifying a certificate revocation list#

The tlsCRLFile option takes a path to a CRL file. It can be passed as a keyword argument:

>>> client = pymongo.MongoClient('',
...                              tls=True,
...                              tlsCRLFile='/path/to/crl.pem')

Or, in the URI:

>>> uri = 'mongodb://'
>>> client = pymongo.MongoClient(uri)


Certificate revocation lists and OCSP cannot be used together.

Client certificates#

PyMongo can be configured to present a client certificate using the tlsCertificateKeyFile option:

>>> client = pymongo.MongoClient('',
...                              tls=True,
...                              tlsCertificateKeyFile='/path/to/client.pem')

If the private key for the client certificate is stored in a separate file, it should be concatenated with the certificate file. For example, to concatenate a PEM-formatted certificate file cert.pem and a PEM-formatted keyfile key.pem into a single file combined.pem, on Unix systems, users can run:

$ cat key.pem cert.pem > combined.pem

PyMongo can be configured with the concatenated certificate keyfile using the tlsCertificateKeyFile option:

>>> client = pymongo.MongoClient('',
...                              tls=True,
...                              tlsCertificateKeyFile='/path/to/combined.pem')

If the private key contained in the certificate keyfile is encrypted, users can provide a password or passphrase to decrypt the encrypted private keys using the tlsCertificateKeyFilePassword option:

>>> client = pymongo.MongoClient('',
...                              tls=True,
...                              tlsCertificateKeyFile='/path/to/combined.pem',
...                              tlsCertificateKeyFilePassword=<passphrase>)

These options can also be passed as part of the MongoDB URI.


Starting with PyMongo 3.11, if PyMongo was installed with the “ocsp” extra:

python -m pip install pymongo[ocsp]

certificate revocation checking is enabled by way of OCSP (Online Certification Status Protocol). MongoDB 4.4+ staples OCSP responses to the TLS handshake which PyMongo will verify, failing the TLS handshake if the stapled OCSP response is invalid or indicates that the peer certificate is revoked.

When connecting to a server version older than 4.4, or when a 4.4+ version of MongoDB does not staple an OCSP response, PyMongo will attempt to connect directly to an OCSP endpoint if the peer certificate specified one. The TLS handshake will only fail in this case if the response indicates that the certificate is revoked. Invalid or malformed responses will be ignored, favoring availability over maximum security.

Troubleshooting TLS Errors#

TLS errors often fall into three categories - certificate verification failure, protocol version mismatch or certificate revocation checking failure. An error message similar to the following means that OpenSSL was not able to verify the server’s certificate:

[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed

This often occurs because OpenSSL does not have access to the system’s root certificates or the certificates are out of date. Linux users should ensure that they have the latest root certificate updates installed from their Linux vendor. macOS users using Python 3.7 or newer downloaded from may have to run a script included with python to install root certificates:

open "/Applications/Python <YOUR PYTHON VERSION>/Install Certificates.command"

Users of older PyPy portable versions may have to set an environment variable to tell OpenSSL where to find root certificates. This is easily done using the certifi module from pypi:

$ pypy -m pip install certifi
$ export SSL_CERT_FILE=$(pypy -c "import certifi; print(certifi.where())")

An error message similar to the following message means that the OpenSSL version used by Python does not support a new enough TLS protocol to connect to the server:

[SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version

Industry best practices recommend, and some regulations require, that older TLS protocols be disabled in some MongoDB deployments. Some deployments may disable TLS 1.0, others may disable TLS 1.0 and TLS 1.1. See the warning earlier in this document for troubleshooting steps and solutions.

An error message similar to the following message means that certificate revocation checking failed:

[('SSL routines', 'tls_process_initial_server_flight', 'invalid status response')]

See OCSP for more details.

Python 3.10+ incompatibilities with TLS/SSL on MongoDB <= 4.0#

Note that changes made to the ssl module in Python 3.10+ may cause incompatibilities with MongoDB <= 4.0. The following are some example errors that may occur with this combination:

SSL handshake failed: localhost:27017: [SSL: SSLV3_ALERT_HANDSHAKE_FAILURE] sslv3 alert handshake failure (_ssl.c:997)
SSL handshake failed: localhost:27017: EOF occurred in violation of protocol (_ssl.c:997)

The MongoDB server logs may show the following error:

2021-06-30T21:22:44.917+0100 E NETWORK  [conn16] SSL: error:1408A0C1:SSL routines:ssl3_get_client_hello:no shared cipher

To resolve this issue, use Python <=3.10, upgrade to MongoDB 4.2+, or install pymongo with the OCSP extra which relies on PyOpenSSL.