[2.2.x] Fixed #31784 -- Fixed crash when sending emails on Python 3.6.11+, 3.7.8+, and 3.8.4+.

Fixed sending emails crash on email addresses with display names longer
then 75 chars on Python 3.6.11+, 3.7.8+, and 3.8.4+.

Wrapped display names were passed to email.headerregistry.Address()
what caused raising an exception because address parts cannot contain
CR or LF.

See https://bugs.python.org/issue39073

Co-Authored-By: Mariusz Felisiak <felisiak.mariusz@gmail.com>

Backport of 96a3ea39ef0790dbc413dde0a3e19f6a769356a2 from master.

3 files changed, 58 insertions, 9 deletions

diff --git a/django/core/mail/message.py b/django/core/mail/message.py
index a0e80acce9..7a3ee799f5 100644
--- a/django/core/mail/message.py
+++ b/django/core/mail/message.py
@@ -10,7 +10,9 @@ from email.mime.base import MIMEBase
 from email.mime.message import MIMEMessage
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
-from email.utils import formatdate, getaddresses, make_msgid, parseaddr
+from email.utils import (
+    formataddr, formatdate, getaddresses, make_msgid, parseaddr,
+)
 from io import BytesIO, StringIO
 from pathlib import Path
 
@@ -103,7 +105,15 @@ def sanitize_address(addr, encoding):
         addr = parseaddr(addr)
     nm, addr = addr
     localpart, domain = None, None
-    nm = Header(nm, encoding).encode()
+    if '\n' in nm or '\r' in nm:
+        raise ValueError('Invalid address; address parts cannot contain newlines.')
+
+    # Avoid UTF-8 encode, if it's possible.
+    try:
+        nm.encode('ascii')
+        nm = Header(nm).encode()
+    except UnicodeEncodeError:
+        nm = Header(nm, encoding).encode()
     try:
         addr.encode('ascii')
     except UnicodeEncodeError:  # IDN or non-ascii in the local part
@@ -112,15 +122,20 @@ def sanitize_address(addr, encoding):
     # An `email.headerregistry.Address` object is used since
     # email.utils.formataddr() naively encodes the name as ascii (see #25986).
     if localpart and domain:
-        address = Address(nm, username=localpart, domain=domain)
-        return str(address)
+        address_parts = localpart + domain
+        if '\n' in address_parts or '\r' in address_parts:
+            raise ValueError('Invalid address; address parts cannot contain newlines.')
+        address = Address(username=localpart, domain=domain)
+        return formataddr((nm, address.addr_spec))
 
     try:
-        address = Address(nm, addr_spec=addr)
+        if '\n' in addr or '\r' in addr:
+            raise ValueError('Invalid address; address parts cannot contain newlines.')
+        address = Address(addr_spec=addr)
     except (InvalidHeaderDefect, NonASCIILocalPartDefect):
         localpart, domain = split_addr(addr, encoding)
-        address = Address(nm, username=localpart, domain=domain)
-    return str(address)
+        address = Address(username=localpart, domain=domain)
+    return formataddr((nm, address.addr_spec))
 
 
 class MIMEMixin:
diff --git a/docs/releases/2.2.15.txt b/docs/releases/2.2.15.txt
index df26962029..d8ed58b596 100644
--- a/docs/releases/2.2.15.txt
+++ b/docs/releases/2.2.15.txt
@@ -4,10 +4,13 @@ Django 2.2.15 release notes
 
 *Expected August 3, 2020*
 
-Django 2.2.15 fixes a bug in 2.2.14.
+Django 2.2.15 fixes two bugs in 2.2.14.
 
 Bugfixes
 ========
 
 * Allowed setting the ``SameSite`` cookie flag in
   :meth:`.HttpResponse.delete_cookie` (:ticket:`31790`).
+
+* Fixed crash when sending emails to addresses with display names longer than
+  75 chars on Python 3.6.11+, 3.7.8+, and 3.8.4+ (:ticket:`31784`).
diff --git a/tests/mail/tests.py b/tests/mail/tests.py
index f06e053074..e62141c040 100644
--- a/tests/mail/tests.py
+++ b/tests/mail/tests.py
@@ -720,7 +720,7 @@ class MailTests(HeadersCheckMixin, SimpleTestCase):
         )
         self.assertEqual(
             sanitize_address(('A name', 'to@example.com'), 'utf-8'),
-            '=?utf-8?q?A_name?= <to@example.com>'
+            'A name <to@example.com>'
         )
 
         # Unicode characters are are supported in RFC-6532.
@@ -732,6 +732,37 @@ class MailTests(HeadersCheckMixin, SimpleTestCase):
             sanitize_address(('Tó Example', 'tó@example.com'), 'utf-8'),
             '=?utf-8?q?T=C3=B3_Example?= <=?utf-8?b?dMOz?=@example.com>'
         )
+        # Addresses with long unicode display names.
+        self.assertEqual(
+            sanitize_address('Tó Example very long' * 4 + ' <to@example.com>', 'utf-8'),
+            '=?utf-8?q?T=C3=B3_Example_very_longT=C3=B3_Example_very_longT=C3='
+            'B3_Example_?=\n'
+            ' =?utf-8?q?very_longT=C3=B3_Example_very_long?= <to@example.com>'
+        )
+        self.assertEqual(
+            sanitize_address(('Tó Example very long' * 4, 'to@example.com'), 'utf-8'),
+            '=?utf-8?q?T=C3=B3_Example_very_longT=C3=B3_Example_very_longT=C3='
+            'B3_Example_?=\n'
+            ' =?utf-8?q?very_longT=C3=B3_Example_very_long?= <to@example.com>'
+        )
+        # Address with long display name and unicode domain.
+        self.assertEqual(
+            sanitize_address(('To Example very long' * 4, 'to@exampl€.com'), 'utf-8'),
+            'To Example very longTo Example very longTo Example very longTo Ex'
+            'ample very\n'
+            ' long <to@xn--exampl-nc1c.com>'
+        )
+
+    def test_sanitize_address_header_injection(self):
+        msg = 'Invalid address; address parts cannot contain newlines.'
+        tests = [
+            ('Name\nInjection', 'to@xample.com'),
+            ('Name', 'to\ninjection@example.com'),
+        ]
+        for email_address in tests:
+            with self.subTest(email_address=email_address):
+                with self.assertRaisesMessage(ValueError, msg):
+                    sanitize_address(email_address, encoding='utf-8')
 
 
 @requires_tz_support