Merge pull request #2246 from half-duplex/ssl-wrap-socket

backends: allow setting TLS version and ciphers

sopel/config/core_section.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from ssl import TLSVersion
+
 from sopel.config.types import (
     BooleanAttribute,
     ChoiceAttribute,
@@ -21,6 +23,20 @@
 """Default URL schemes allowed for URLs."""
 
 
+def _parse_ssl_version(var: str) -> TLSVersion:
+    """Parse an ssl_version config variable.
+
+    :param var: The input string, e.g. "TLSv1_3".
+    :return: The TLSVersion object for that version.
+    """
+    try:
+        return TLSVersion[var]
+    except KeyError:
+        raise ValueError(
+            "'{}' is not a valid TLSVersion. Try e.g. TLSv1_3'".format(var)
+        )
+
+
 def configure(config):
     """Interactively configure the bot's ``[core]`` config section.
 
@@ -1187,6 +1203,75 @@ def homedir(self):
 
     """
 
+    ssl_ciphers = ListAttribute(
+        'ssl_ciphers',
+        default=[
+            "ECDHE-ECDSA-AES128-GCM-SHA256",
+            "ECDHE-RSA-AES128-GCM-SHA256",
+            "ECDHE-ECDSA-AES256-GCM-SHA384",
+            "ECDHE-RSA-AES256-GCM-SHA384",
+            "ECDHE-ECDSA-CHACHA20-POLY1305",
+            "ECDHE-RSA-CHACHA20-POLY1305",
+            "DHE-RSA-AES128-GCM-SHA256",
+            "DHE-RSA-AES256-GCM-SHA384",
+        ],
+    )
+    """The cipher suites enabled for SSL/TLS connections.
+
+    :default: ``ECDHE-ECDSA-AES128-GCM-SHA256
+                ECDHE-RSA-AES128-GCM-SHA256
+                ECDHE-ECDSA-AES256-GCM-SHA384
+                ECDHE-RSA-AES256-GCM-SHA384
+                ECDHE-ECDSA-CHACHA20-POLY1305
+                ECDHE-RSA-CHACHA20-POLY1305
+                DHE-RSA-AES128-GCM-SHA256
+                DHE-RSA-AES256-GCM-SHA384``
+
+    The default is the `Mozilla Intermediate configuration`__ as of February
+    2022. This parameter is in OpenSSL format; see the `ciphers manual page`__
+    for your version. This setting cannot be used to configure TLS 1.3.
+
+    .. __: https://wiki.mozilla.org/Security/Server_Side_TLS
+    .. __: https://www.openssl.org/docs/manmaster/man1/ciphers.html
+
+    .. code-block:: ini
+
+        ssl_ciphers =
+            ECDSA+AES256
+            !SHA1
+
+    .. note::
+
+        Cipher selection is also subject to the available SSL/TLS versions;
+        see :attr:`ssl_minimum_version`.
+
+    """
+
+    ssl_minimum_version = ValidatedAttribute(
+        'ssl_minimum_version',
+        default=TLSVersion.TLSv1_2,
+        parse=_parse_ssl_version,
+        serialize=lambda ver: ver.name,
+    )
+    """The minimum version allowed for SSL/TLS connections.
+
+    :default: ``TLSv1_2``
+
+    You should not set this lower than the default unless the server does not
+    support modern versions. Set this to a :class:`~ssl.TLSVersion` value,
+    e.g. ``TLSv1`` or ``TLSv1_3``.
+
+    .. code-block:: ini
+
+        ssl_minimum_version = TLSv1_3
+
+    .. note::
+
+        To use insecure SSL/TLS versions, you may also need to enable
+        insecure cipher suites. See :attr:`ssl_ciphers`.
+
+    """
+
     use_ssl = BooleanAttribute('use_ssl', default=True)
     """Whether to use a SSL/TLS encrypted connection.
 

sopel/irc/__init__.py

@@ -231,6 +231,8 @@ def get_irc_backend(
             keyfile=self.settings.core.client_cert_file,
             verify_ssl=self.settings.core.verify_ssl,
             ca_certs=self.settings.core.ca_certs,
+            ssl_ciphers=self.settings.core.ssl_ciphers,
+            ssl_minimum_version=self.settings.core.ssl_minimum_version,
         )
 
     def run(self, host: str, port: int = 6667) -> None:

sopel/irc/backends.py

@@ -8,7 +8,7 @@
 import signal
 import ssl
 import threading
-from typing import Dict, Optional, Tuple, TYPE_CHECKING
+from typing import Dict, List, Optional, Tuple, TYPE_CHECKING
 
 from .abstract_backends import AbstractIRCBackend
 
@@ -54,6 +54,8 @@ class AsyncioBackend(AbstractIRCBackend):
                        ``use_ssl`` is not ``True``
     :param ca_certs: optional location to the CA certificates; ignored if
                     ``verify_ssl`` is ``False``
+    :param ssl_ciphers: the OpenSSL cipher suites to use
+    :param ssl_minimum_version: the lowest SSL/TLS version to accept
     """
     def __init__(
         self,
@@ -68,6 +70,8 @@ def __init__(
         keyfile: Optional[str] = None,
         verify_ssl: bool = True,
         ca_certs: Optional[str] = None,
+        ssl_ciphers: Optional[List[str]] = None,
+        ssl_minimum_version: Optional[ssl.TLSVersion] = None,
         **kwargs,
     ):
         super().__init__(bot)
@@ -80,6 +84,8 @@ def __init__(
         self._keyfile: Optional[str] = keyfile
         self._verify_ssl: bool = verify_ssl
         self._ca_certs: Optional[str] = ca_certs
+        self._ssl_ciphers: str = ":".join(ssl_ciphers)
+        self._ssl_minimum_version: ssl.TLSVersion = ssl_minimum_version
 
         # timeout configuration
         self._server_timeout: float = float(server_timeout or 120)
@@ -263,6 +269,8 @@ def get_connection_kwargs(self) -> Dict:
 
         if self._use_ssl:
             ssl_context = ssl.create_default_context(ssl.Purpose.SERVER_AUTH)
+            ssl_context.minimum_version = self._ssl_minimum_version
+            ssl_context.set_ciphers(self._ssl_ciphers)
             if self._certfile is not None:
                 # load_cert_chain requires a certfile (cannot be None)
                 ssl_context.load_cert_chain(