https://github.com/python/cpython/commit/a62ba52f1439c1f878a3ff9b8544caf9aee... commit: a62ba52f1439c1f878a3ff9b8544caf9aeef9b90 branch: main author: RanKKI <hliu86.me@gmail.com> committer: bitdancer <rdmurray@bitdance.com> date: 2025-01-05T20:32:16-05:00 summary: gh-98188: Fix EmailMessage.get_payload to decode data when CTE value has extra text (#127547) Up to this point message handling has been very strict with regards to content encoding values: mixed case was accepted, but trailing blanks or other text would cause decoding failure, even if the first token was a valid encoding. By Postel's Rule we should go ahead and decode as long as we can recognize that first token. We have not thought of any security or backward compatibility concerns with this fix. This fix does introduce a new technique/pattern to the Message code: we look to see if the header has a 'cte' attribute, and if so we use that. This effectively promotes the header API exposed by HeaderRegistry to an API that any header parser "should" support. This seems like a reasonable thing to do. It is not, however, a requirement, as the string value of the header is still used if there is no cte attribute. The full fix (ignore any trailing blanks or blank-separated trailing text) applies only to the non-compat32 API. compat32 is only fixed to the extent that it now ignores trailing spaces. Note that the HeaderRegistry parsing still records a HeaderDefect if there is extra text. Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com> files: A Misc/NEWS.d/next/Library/2024-12-03-14-45-16.gh-issue-98188.GX9i2b.rst M Lib/email/message.py M Lib/test/test_email/test_email.py M Lib/test/test_email/test_headerregistry.py M Misc/ACKS diff --git a/Lib/email/message.py b/Lib/email/message.py index a58afc5fe5f68e..87fcab68868d46 100644 --- a/Lib/email/message.py +++ b/Lib/email/message.py @@ -286,8 +286,12 @@ def get_payload(self, i=None, decode=False): if i is not None and not isinstance(self._payload, list): raise TypeError('Expected list, got %s' % type(self._payload)) payload = self._payload - # cte might be a Header, so for now stringify it. - cte = str(self.get('content-transfer-encoding', '')).lower() + cte = self.get('content-transfer-encoding', '') + if hasattr(cte, 'cte'): + cte = cte.cte + else: + # cte might be a Header, so for now stringify it. + cte = str(cte).strip().lower() # payload may be bytes here. if not decode: if isinstance(payload, str) and utils._has_surrogates(payload): diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py index abe9ef2e94409f..2deb35721576b8 100644 --- a/Lib/test/test_email/test_email.py +++ b/Lib/test/test_email/test_email.py @@ -810,6 +810,16 @@ def test_unicode_body_defaults_to_utf8_encoding(self): w4kgdGVzdGFiYwo= """)) + def test_string_payload_with_base64_cte(self): + msg = email.message_from_string(textwrap.dedent("""\ + Content-Transfer-Encoding: base64 + + SGVsbG8uIFRlc3Rpbmc= + """), policy=email.policy.default) + self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing") + self.assertDefectsEqual(msg['content-transfer-encoding'].defects, []) + + # Test the email.encoders module class TestEncoders(unittest.TestCase): @@ -2352,6 +2362,40 @@ def test_missing_header_body_separator(self): self.assertDefectsEqual(msg.defects, [errors.MissingHeaderBodySeparatorDefect]) + def test_string_payload_with_extra_space_after_cte(self): + # https://github.com/python/cpython/issues/98188 + cte = "base64 " + msg = email.message_from_string(textwrap.dedent(f"""\ + Content-Transfer-Encoding: {cte} + + SGVsbG8uIFRlc3Rpbmc= + """), policy=email.policy.default) + self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing") + self.assertDefectsEqual(msg['content-transfer-encoding'].defects, []) + + def test_string_payload_with_extra_text_after_cte(self): + msg = email.message_from_string(textwrap.dedent("""\ + Content-Transfer-Encoding: base64 some text + + SGVsbG8uIFRlc3Rpbmc= + """), policy=email.policy.default) + self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing") + cte = msg['content-transfer-encoding'] + self.assertDefectsEqual(cte.defects, [email.errors.InvalidHeaderDefect]) + + def test_string_payload_with_extra_space_after_cte_compat32(self): + cte = "base64 " + msg = email.message_from_string(textwrap.dedent(f"""\ + Content-Transfer-Encoding: {cte} + + SGVsbG8uIFRlc3Rpbmc= + """), policy=email.policy.compat32) + pasted_cte = msg['content-transfer-encoding'] + self.assertEqual(pasted_cte, cte) + self.assertEqual(msg.get_payload(decode=True), b"Hello. Testing") + self.assertDefectsEqual(msg.defects, []) + + # Test RFC 2047 header encoding and decoding class TestRFC2047(TestEmailBase): diff --git a/Lib/test/test_email/test_headerregistry.py b/Lib/test/test_email/test_headerregistry.py index 4c0523f410332f..ff7a6da644d572 100644 --- a/Lib/test/test_email/test_headerregistry.py +++ b/Lib/test/test_email/test_headerregistry.py @@ -837,6 +837,11 @@ def cte_as_value(self, '7bit', [errors.InvalidHeaderDefect]), + 'extra_space_after_cte': ( + 'base64 ', + 'base64', + []), + } diff --git a/Misc/ACKS b/Misc/ACKS index c6e53317b37d78..d7585c16c8169c 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -1129,6 +1129,7 @@ Gregor Lingl Everett Lipman Mirko Liss Alexander Liu +Hui Liu Yuan Liu Nick Lockwood Stephanie Lockwood diff --git a/Misc/NEWS.d/next/Library/2024-12-03-14-45-16.gh-issue-98188.GX9i2b.rst b/Misc/NEWS.d/next/Library/2024-12-03-14-45-16.gh-issue-98188.GX9i2b.rst new file mode 100644 index 00000000000000..30ab8cfc3f0bc6 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2024-12-03-14-45-16.gh-issue-98188.GX9i2b.rst @@ -0,0 +1,3 @@ +Fix an issue in :meth:`email.message.Message.get_payload` where data +cannot be decoded if the Content Transfer Encoding mechanism contains +trailing whitespaces or additional junk text. Patch by Hui Liu.