bpo-34155: Dont parse domains containing @ (GH-13079)

Before:

        >>> email.message_from_string('From: [email protected]@important.com', policy=email.policy.default)['from'].addresses
        (Address(display_name='', username='a', domain='malicious.org'),)

        >>> parseaddr('[email protected]@important.com')
        ('', '[email protected]')

    After:

        >>> email.message_from_string('From: [email protected]@important.com', policy=email.policy.default)['from'].addresses
        (Address(display_name='', username='', domain=''),)

        >>> parseaddr('[email protected]@important.com')
        ('', 'a@')

https://bugs.python.org/issue34155
(cherry picked from commit 8cb65d1)

Co-authored-by: jpic <[email protected]>

Author: miss-islington

Lib/email/_header_value_parser.py

@@ -1566,6 +1566,8 @@ def get_domain(value):
         token, value = get_dot_atom(value)
     except errors.HeaderParseError:
         token, value = get_atom(value)
+    if value and value[0] == '@':
+        raise errors.HeaderParseError('Invalid Domain')
     if leader is not None:
         token[:0] = [leader]
     domain.append(token)

Lib/email/_parseaddr.py

@@ -379,7 +379,12 @@ def getaddrspec(self):
         aslist.append('@')
         self.pos += 1
         self.gotonext()
-        return EMPTYSTRING.join(aslist) + self.getdomain()
+        domain = self.getdomain()
+        if not domain:
+            # Invalid domain, return an empty address instead of returning a
+            # local part to denote failed parsing.
+            return EMPTYSTRING
+        return EMPTYSTRING.join(aslist) + domain
 
     def getdomain(self):
         """Get the complete domain name from an address."""
@@ -394,6 +399,10 @@ def getdomain(self):
             elif self.field[self.pos] == '.':
                 self.pos += 1
                 sdlist.append('.')
+            elif self.field[self.pos] == '@':
+                # bpo-34155: Don't parse domains with two `@` like
+                # `[email protected]@important.com`.
+                return EMPTYSTRING
             elif self.field[self.pos] in self.atomends:
                 break
             else:

Lib/test/test_email/test__header_value_parser.py

@@ -1428,6 +1428,16 @@ def test_get_addr_spec_dot_atom(self):
         self.assertEqual(addr_spec.domain, 'example.com')
         self.assertEqual(addr_spec.addr_spec, '[email protected]')
 
+    def test_get_addr_spec_multiple_domains(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_addr_spec('[email protected]@example.com')
+
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_addr_spec('star@[email protected]')
+
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_addr_spec('[email protected]@example.com')
+
     # get_obs_route
 
     def test_get_obs_route_simple(self):

Lib/test/test_email/test_email.py

@@ -3041,6 +3041,20 @@ def test_parseaddr_empty(self):
         self.assertEqual(utils.parseaddr('<>'), ('', ''))
         self.assertEqual(utils.formataddr(utils.parseaddr('<>')), '')
 
+    def test_parseaddr_multiple_domains(self):
+        self.assertEqual(
+            utils.parseaddr('a@b@c'),
+            ('', '')
+        )
+        self.assertEqual(
+            utils.parseaddr('[email protected]@c'),
+            ('', '')
+        )
+        self.assertEqual(
+            utils.parseaddr('[email protected]@c'),
+            ('', '')
+        )
+
     def test_noquote_dump(self):
         self.assertEqual(
             utils.formataddr(('A Silly Person', '[email protected]')),

Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst

@@ -0,0 +1 @@
+Fix parsing of invalid email addresses with more than one ``@`` (e.g. a@[email protected].) to not return the part before 2nd ``@`` as valid email address. Patch by maxking & jpic.