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
(cherry picked from commit 8cb65d1381b027f0b09ee36bfed7f35bb4dec9a9)

Co-authored-by: jpic <jpic@users.noreply.github.com>

2 files changed, 12 insertions, 1 deletions

diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index 7dfd978..a930792 100644
--- a/Lib/email/_header_value_parser.py
+++ b/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)
diff --git a/Lib/email/_parseaddr.py b/Lib/email/_parseaddr.py
index cdfa372..41ff6f8 100644
--- a/Lib/email/_parseaddr.py
+++ b/Lib/email/_parseaddr.py
@@ -379,7 +379,12 @@ class AddrlistClass:
         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 @@ class AddrlistClass:
             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: