commit 8cb65d1381b027f0b09ee36bfed7f35bb4dec9a9
author jpic <jpic@users.noreply.github.com> Wed Jul 17 23:54:25 2019 +0200
committer Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Wed Jul 17 14:54:25 2019 -0700
tree 66906fde428f0af62b753d529cd28a87c9e7438c
parent 719a062bcb7b08a56e6576dcd75f4244e6053209

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

Lib/email/_parseaddr.py

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 @@
         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 @@
             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: