Improper Certificate Validation Using nntplib

The Python class nntplib.NNTP_SSL by default creates an SSL context that does not verify the server's certificate if the context parameter is unset or has a value of None. This means that an attacker can easily impersonate a legitimate server and fool your application into connecting to it.

If you use nntplib.NNTP_SSL or starttls without a context set, you are opening your application up to a number of security risks, including:

  • Man-in-the-middle attacks
  • Session hijacking
  • Data theft

Example

import nntplib


with nntplib.NNTP_SSL("news.gmane.io") as n:
    n.login("user", "password")
    n.group("gmane.comp.python.committers")

Remediation

Set the value of the context keyword argument to ssl.create_default_context() to ensure the connection is fully verified.

import nntplib
import ssl


with nntplib.NNTP_SSL(
    "news.gmane.io",
    context=ssl.create_default_context(),
) as n:
    n.login("user", "password")
    n.group("gmane.comp.python.committers")

See also

New in version 0.3.14