Merge pull request from GHSA-pr2m-px7j-xg65

* SMTP Smuggling Fix

Adapted adherence to RFC 5321 § 2.3.8 to fix SMTP smuggling issues (https://www.rfc-editor.org/rfc/rfc5321#section-2.3.8)

* Apply suggestions from code review

Co-authored-by: Sam Bull <git@sambull.org>

* Add files via upload

* Update test_smtpsmuggling.py

---------

Co-authored-by: Sam Bull <git@sambull.org>

aiosmtpd/smtp.py

@@ -87,7 +87,7 @@ class _DataState(enum.Enum):
 EMPTY_BARR = bytearray()
 EMPTYBYTES = b''
 MISSING = _Missing.MISSING
-NEWLINE = '\n'
+NEWLINE = '\r\n'
 VALID_AUTHMECH = re.compile(r"[A-Z0-9_-]+\Z")
 
 # https://tools.ietf.org/html/rfc3207.html#page-3
@@ -1427,9 +1427,10 @@ async def smtp_DATA(self, arg: str) -> None:
             # Since eof_received cancels this coroutine,
             # readuntil() can never raise asyncio.IncompleteReadError.
             try:
-                line: bytes = await self._reader.readuntil()
+                # https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.8
+                line: bytes = await self._reader.readuntil(b'\r\n')
                 log.debug('DATA readline: %s', line)
-                assert line.endswith(b'\n')
+                assert line.endswith(b'\r\n')
             except asyncio.CancelledError:
                 # The connection got reset during the DATA command.
                 log.info('Connection lost during DATA')
@@ -1446,7 +1447,7 @@ async def smtp_DATA(self, arg: str) -> None:
                 data *= 0
                 # Drain the stream anyways
                 line = await self._reader.read(e.consumed)
-                assert not line.endswith(b'\n')
+                assert not line.endswith(b'\r\n')
             # A lone dot in a line signals the end of DATA.
             if not line_fragments and line == b'.\r\n':
                 break
@@ -1458,7 +1459,7 @@ async def smtp_DATA(self, arg: str) -> None:
                 # Discard data immediately to prevent memory pressure
                 data *= 0
             line_fragments.append(line)
-            if line.endswith(b'\n'):
+            if line.endswith(b'\r\n'):
                 # Record data only if state is "NOMINAL"
                 if state == _DataState.NOMINAL:
                     line = EMPTY_BARR.join(line_fragments)

aiosmtpd/tests/test_smtpsmuggling.py

@@ -0,0 +1,79 @@
+# Copyright 2014-2021 The aiosmtpd Developers
+# SPDX-License-Identifier: Apache-2.0
+
+"""Test SMTP smuggling."""
+
+from email.mime.text import MIMEText
+from smtplib import SMTP, SMTP_SSL
+from typing import Generator, Union
+
+import pytest
+import smtplib
+
+from aiosmtpd.controller import Controller
+from aiosmtpd.testing.helpers import ReceivingHandler
+from aiosmtpd.testing.statuscodes import SMTP_STATUS_CODES as S
+
+from aiosmtpd.smtp import SMTP as Server
+from aiosmtpd.smtp import Session as ServerSession
+from aiosmtpd.smtp import Envelope
+
+from .conftest import Global, controller_data, handler_data
+
+from aiosmtpd.testing.helpers import (
+    ReceivingHandler
+)
+
+def new_data(self, msg):
+        self.putcmd("data")
+
+        (code, repl) = self.getreply()
+        if self.debuglevel > 0:
+            self._print_debug('data:', (code, repl))
+        if code != 354:
+            raise SMTPDataError(code, repl)
+        else:
+            ##### Patching input encoding so we can send raw messages
+            #if isinstance(msg, str):
+            #    msg = smtplib._fix_eols(msg).encode('ascii')
+            #q = smtplib._quote_periods(msg)
+            #if q[-2:] != smtplib.bCRLF:
+            #    q = q + smtplib.bCRLF
+            #q = q + b"." + smtplib.bCRLF
+            q = msg
+            self.send(q)
+            (code, msg) = self.getreply()
+            if self.debuglevel > 0:
+                self._print_debug('data:', (code, msg))
+            return (code, msg)
+
+def return_unchanged(data):
+    return data
+
+class TestSmuggling:
+    @handler_data(class_=ReceivingHandler)
+    def test_smtp_smuggling(self, plain_controller, client):
+        smtplib._fix_eols = return_unchanged
+        smtplib._quote_periods = return_unchanged
+        smtplib.SMTP.data = new_data
+
+        handler = plain_controller.handler
+        sender = "sender@example.com"
+        recipients = ["rcpt1@example.com"]
+        resp = client.helo("example.com")
+        assert resp == S.S250_FQDN
+        # Trying SMTP smuggling with a fake \n.\r\n end-of-data sequence.
+        message_data = b"""\
+From: Anne Person <anne@example.com>\r\n\
+To: Bart Person <bart@example.com>\r\n\
+Subject: A test\r\n\
+Message-ID: <ant>\r\n\
+\r\n\
+Testing\
+\n.\r\n\
+NO SMUGGLING
+\r\n.\r\n\
+"""
+        results = client.sendmail(sender, recipients, message_data)
+        client.quit()
+        assert b"NO SMUGGLING" in handler.box[0].content