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

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* 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
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2
Lib/email/feedparser.py
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@ -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)