bpo-30835: email: Fix AttributeError when parsing invalid CTE (GH-13598)

* bpo-30835: email: Fix AttributeError when parsing invalid Content-Transfer-Encoding

Parsing an email containing a multipart Content-Type, along with a
Content-Transfer-Encoding containing an invalid (non-ASCII-decodable) byte
will fail. email.feedparser.FeedParser._parsegen() gets the header and
attempts to convert it to lowercase before comparing it with the accepted
encodings, but as the header contains an invalid byte, it's returned as a
Header object rather than a str.

Cast the Content-Transfer-Encoding header to a str to avoid this.

Found using the AFL fuzzer.

Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Donnellan <andrew@donnellan.id.au>

* Add email and NEWS entry for the bugfix.
This commit is contained in:
Abhilash Raj 2019-06-04 14:00:47 -04:00 committed by Barry Warsaw
parent 46d88a1131
commit aa79707262
3 changed files with 13 additions and 1 deletions

View File

@ -320,7 +320,7 @@ class FeedParser:
self._cur.set_payload(EMPTYSTRING.join(lines))
return
# Make sure a valid content type was specified per RFC 2045:6.4.
if (self._cur.get('content-transfer-encoding', '8bit').lower()
if (str(self._cur.get('content-transfer-encoding', '8bit')).lower()
not in ('7bit', '8bit', 'binary')):
defect = errors.InvalidMultipartContentTransferEncodingDefect()
self.policy.handle_defect(self._cur, defect)

View File

@ -1466,6 +1466,15 @@ Blah blah blah
g.flatten(msg)
self.assertEqual(b.getvalue(), source + b'>From R\xc3\xb6lli\n')
def test_mutltipart_with_bad_bytes_in_cte(self):
# bpo30835
source = textwrap.dedent("""\
From: aperson@example.com
Content-Type: multipart/mixed; boundary="1"
Content-Transfer-Encoding: \xc8
""").encode('utf-8')
msg = email.message_from_bytes(source)
# Test the basic MIMEAudio class
class TestMIMEAudio(unittest.TestCase):

View File

@ -0,0 +1,3 @@
Fixed a bug in email parsing where a message with invalid bytes in
content-transfer-encoding of a multipart message can cause an AttributeError.
Patch by Andrew Donnellan.