CVE-2019-16056: Insufficient Information (NVD-CWE-noinfo)
value: An issue was discovered in Python through 2.7.16, 3.x through 3.5.7, 3.6.x through 3.6.9, and 3.7.x through 3.7.4. The email module wrongly parses email addresses that contain multiple @ characters. An application that uses the email module and implements some kind of checks on the From/To headers of a message could be tricked into accepting an email address that should be denied. An attack may be the same as in CVE-2019-11340; however, this CVE applies to Python more generally.
CWE description: There is insufficient information about the issue to classify it; details are unkown or unspecified.
CVSS v3 base score: 7.5
Published: 2019-09-06T18:15Z
Repository: https://github.com/python/cpython
Language: Python
Files changed: Lib/email/_header_value_parser.py, Lib/email/_parseaddr.py, Lib/test/test_email/test__header_value_parser.py, Lib/test/test_email/test_email.py, Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst
Commit date: 2019-07-17 14:54:25 -0700
Commit message: bpo-34155: Dont parse domains containing @ (GH-13079)



Before:
    
        >>> email.message_from_string('From: a@malicious.org@important.com', policy=email.policy.default)['from'].addresses
        (Address(display_name='', username='a', domain='malicious.org'),)
    
        >>> parseaddr('a@malicious.org@important.com')
        ('', 'a@malicious.org')
    
    After:
    
        >>> email.message_from_string('From: a@malicious.org@important.com', policy=email.policy.default)['from'].addresses
        (Address(display_name='', username='', domain=''),)
    
        >>> parseaddr('a@malicious.org@important.com')
        ('', 'a@')




https://bugs.python.org/issue34155
Diff: diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index daff57b9cfa..641e0979f3d 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -1585,10 +1585,12 @@ def get_domain(value):
         return domain, value
     try:
         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)
     if value and value[0] == '.':
         domain.defects.append(errors.ObsoleteHeaderDefect(
diff --git a/Lib/email/_parseaddr.py b/Lib/email/_parseaddr.py
index cdfa3729adc..41ff6f8c000 100644
--- a/Lib/email/_parseaddr.py
+++ b/Lib/email/_parseaddr.py
@@ -377,11 +377,16 @@ def getaddrspec(self):
             return EMPTYSTRING.join(aslist)
 
         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."""
         sdlist = []
         while self.pos < len(self.field):
@@ -392,10 +397,14 @@ def getdomain(self):
             elif self.field[self.pos] == '[':
                 sdlist.append(self.getdomainliteral())
             elif self.field[self.pos] == '.':
                 self.pos += 1
                 sdlist.append('.')
+            elif self.field[self.pos] == '@':
+                # bpo-34155: Don't parse domains with two `@` like
+                # `a@malicious.org@important.com`.
+                return EMPTYSTRING
             elif self.field[self.pos] in self.atomends:
                 break
             else:
                 sdlist.append(self.getatom())
         return EMPTYSTRING.join(sdlist)
diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py
index 4fa56b16c47..877cd3effe1 100644
--- a/Lib/test/test_email/test__header_value_parser.py
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -1446,10 +1446,20 @@ def test_get_addr_spec_dot_atom(self):
             '')
         self.assertEqual(addr_spec.local_part, 'star.a.star')
         self.assertEqual(addr_spec.domain, 'example.com')
         self.assertEqual(addr_spec.addr_spec, 'star.a.star@example.com')
 
+    def test_get_addr_spec_multiple_domains(self):
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_addr_spec('star@a.star@example.com')
+
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_addr_spec('star@a@example.com')
+
+        with self.assertRaises(errors.HeaderParseError):
+            parser.get_addr_spec('star@172.17.0.1@example.com')
+
     # get_obs_route
 
     def test_get_obs_route_simple(self):
         obs_route = self._test_get_x(parser.get_obs_route,
             '@example.com, @two.example.com:',
diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index c29cc56203b..aa775881c55 100644
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -3039,10 +3039,24 @@ def test_parsedate_y2k(self):
 
     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('a@b.c@c'),
+            ('', '')
+        )
+        self.assertEqual(
+            utils.parseaddr('a@172.17.0.1@c'),
+            ('', '')
+        )
+
     def test_noquote_dump(self):
         self.assertEqual(
             utils.formataddr(('A Silly Person', 'person@dom.ain')),
             'A Silly Person <person@dom.ain>')
 
diff --git a/Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst b/Misc/NEWS.d/next/Security/2019-05-04-13-33-37.bpo-34155.MJll68.rst
new file mode 100644
index 00000000000..50292e29ed1
--- /dev/null
+++ b/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@b@c.com.) to not return the part before 2nd ``@`` as valid email address. Patch by maxking & jpic.

Vulnerable code:         return EMPTYSTRING.join(aslist) + self.getdomain()
Fixed code:     if value and value[0] == '@':
        raise errors.HeaderParseError('Invalid Domain')
        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
            elif self.field[self.pos] == '@':
                # bpo-34155: Don't parse domains with two `@` like
                # `a@malicious.org@important.com`.
                return EMPTYSTRING
    def test_get_addr_spec_multiple_domains(self):
        with self.assertRaises(errors.HeaderParseError):
            parser.get_addr_spec('star@a.star@example.com')

        with self.assertRaises(errors.HeaderParseError):
            parser.get_addr_spec('star@a@example.com')

        with self.assertRaises(errors.HeaderParseError):
            parser.get_addr_spec('star@172.17.0.1@example.com')

    def test_parseaddr_multiple_domains(self):
        self.assertEqual(
            utils.parseaddr('a@b@c'),
            ('', '')
        )
        self.assertEqual(
            utils.parseaddr('a@b.c@c'),
            ('', '')
        )
        self.assertEqual(
            utils.parseaddr('a@172.17.0.1@c'),
            ('', '')
        )

Fix parsing of invalid email addresses with more than one ``@`` (e.g. a@b@c.com.) to not return the part before 2nd ``@`` as valid email address. Patch by maxking & jpic.