Fix for CVE-2023-40217

Cherry picked b4bcc06 for SSL

Author: rickprice

Doc/whatsnew/3.7.rst

@@ -2645,3 +2645,20 @@ characters. Leading WHATWG C0 control and space characters are now stripped
 from the URL. This is a mitigation for `CVE-2023-24329
 <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-24329>`_.
 
+Notable security feature in 3.7.17.2
+==================================
+
+email.utils.getaddresses and email.utils.parseaddr now return
+``('', '')`` 2-tuples in more situations where invalid email addresses are
+encountered instead of potentially inaccurate values.
+(Contributed by Thomas Dwyer for :gh:`102988` to ameliorate CVE-2023-27043.)
+
+
+Fixed an issue where instances of :class:`ssl.SSLSocket` were vulnerable to
+a bypass of the TLS handshake and included protections (like certificate
+verification) and treating sent unencrypted data as if it were
+post-handshake TLS encrypted data.  Security issue reported as
+`CVE-2023-40217
+<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-40217>`_ by Aapo
+Oksman. Patch by Gregory P. Smith.
+

Lib/ssl.py

@@ -832,7 +832,7 @@ def _create(cls, sock, server_side=False, do_handshake_on_connect=True,
         )
         self = cls.__new__(cls, **kwargs)
         super(SSLSocket, self).__init__(**kwargs)
-        self.settimeout(sock.gettimeout())
+        sock_timeout = sock.gettimeout()
         sock.detach()
 
         self._context = context
@@ -851,9 +851,38 @@ def _create(cls, sock, server_side=False, do_handshake_on_connect=True,
             if e.errno != errno.ENOTCONN:
                 raise
             connected = False
+            blocking = self.getblocking()
+            self.setblocking(False)
+            try:
+                # We are not connected so this is not supposed to block, but
+                # testing revealed otherwise on macOS and Windows so we do
+                # the non-blocking dance regardless. Our raise when any data
+                # is found means consuming the data is harmless.
+                notconn_pre_handshake_data = self.recv(1)
+            except OSError as e:
+                # EINVAL occurs for recv(1) on non-connected on unix sockets.
+                if e.errno not in (errno.ENOTCONN, errno.EINVAL):
+                    raise
+                notconn_pre_handshake_data = b''
+            self.setblocking(blocking)
+            if notconn_pre_handshake_data:
+                # This prevents pending data sent to the socket before it was
+                # closed from escaping to the caller who could otherwise
+                # presume it came through a successful TLS connection.
+                reason = "Closed before TLS handshake with data in recv buffer."
+                notconn_pre_handshake_data_error = SSLError(e.errno, reason)
+                # Add the SSLError attributes that _ssl.c always adds.
+                notconn_pre_handshake_data_error.reason = reason
+                notconn_pre_handshake_data_error.library = None
+                try:
+                    self.close()
+                except OSError:
+                    pass
+                raise notconn_pre_handshake_data_error
         else:
             connected = True
 
+        self.settimeout(sock_timeout)  # Must come after setblocking() calls.
         self._connected = connected
         if connected:
             # create the SSL object