https://github.com/python/cpython/commit/295b53df2aa18deb625a7da41f7e4babfe6ef34b
commit: 295b53df2aa18deb625a7da41f7e4babfe6ef34b
branch: main
author: Mike Edmunds <medmu...@gmail.com>
committer: encukou <encu...@gmail.com>
date: 2025-03-18T12:07:17+01:00
summary:
gh-121284: Fix email address header folding with parsed encoded-word (GH-122754)
Email generators using email.policy.default may convert an RFC 2047
encoded-word to unencoded form during header refolding. In a structured
header, this could allow 'specials' chars outside a quoted-string,
leading to invalid address headers and enabling spoofing. This change
ensures a parsed encoded-word that contains specials is kept as an
encoded-word while the header is refolded.
[Better fix from @bitdancer.]
---------
Co-authored-by: R David Murray <rdmur...@bitdance.com>
Co-authored-by: Petr Viktorin <encu...@gmail.com>
files:
A Misc/NEWS.d/next/Security/2024-08-06-12-27-34.gh-issue-121284.8rwPxe.rst
M Lib/email/_header_value_parser.py
M Lib/test/test_email/test__header_value_parser.py
diff --git a/Lib/email/_header_value_parser.py
b/Lib/email/_header_value_parser.py
index 3d845c09d415f6..9a51b9437333db 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -1053,7 +1053,7 @@ def get_fws(value):
fws = WhiteSpaceTerminal(value[:len(value)-len(newvalue)], 'fws')
return fws, newvalue
-def get_encoded_word(value):
+def get_encoded_word(value, terminal_type='vtext'):
""" encoded-word = "=?" charset "?" encoding "?" encoded-text "?="
"""
@@ -1092,7 +1092,7 @@ def get_encoded_word(value):
ew.append(token)
continue
chars, *remainder = _wsp_splitter(text, 1)
- vtext = ValueTerminal(chars, 'vtext')
+ vtext = ValueTerminal(chars, terminal_type)
_validate_xtext(vtext)
ew.append(vtext)
text = ''.join(remainder)
@@ -1134,7 +1134,7 @@ def get_unstructured(value):
valid_ew = True
if value.startswith('=?'):
try:
- token, value = get_encoded_word(value)
+ token, value = get_encoded_word(value, 'utext')
except _InvalidEwError:
valid_ew = False
except errors.HeaderParseError:
@@ -1163,7 +1163,7 @@ def get_unstructured(value):
# the parser to go in an infinite loop.
if valid_ew and rfc2047_matcher.search(tok):
tok, *remainder = value.partition('=?')
- vtext = ValueTerminal(tok, 'vtext')
+ vtext = ValueTerminal(tok, 'utext')
_validate_xtext(vtext)
unstructured.append(vtext)
value = ''.join(remainder)
@@ -2813,7 +2813,7 @@ def _refold_parse_tree(parse_tree, *, policy):
continue
tstr = str(part)
if not want_encoding:
- if part.token_type == 'ptext':
+ if part.token_type in ('ptext', 'vtext'):
# Encode if tstr contains special characters.
want_encoding = not SPECIALSNL.isdisjoint(tstr)
else:
diff --git a/Lib/test/test_email/test__header_value_parser.py
b/Lib/test/test_email/test__header_value_parser.py
index d60a7039f9d4c6..ac12c3b2306f7d 100644
--- a/Lib/test/test_email/test__header_value_parser.py
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -3076,6 +3076,31 @@ def test_address_list_with_unicode_names_in_quotes(self):
'=?utf-8?q?H=C3=BCbsch?= Kaktus <beauti...@example.com>,\n'
' =?utf-8?q?bei=C3=9Ft_bei=C3=9Ft?= <bi...@example.com>\n')
+ def test_address_list_with_specials_in_encoded_word(self):
+ # An encoded-word parsed from a structured header must remain
+ # encoded when it contains specials. Regression for gh-121284.
+ policy = self.policy.clone(max_line_length=40)
+ cases = [
+ # (to, folded)
+ ('=?utf-8?q?A_v=C3=A9ry_long_name_with=2C_comma?=
<t...@example.com>',
+ 'A =?utf-8?q?v=C3=A9ry_long_name_with?=\n'
+ ' =?utf-8?q?=2C?= comma <t...@example.com>\n'),
+ ('=?utf-8?q?This_long_name_does_not_need_encoded=2Dword?=
<t...@example.com>',
+ 'This long name does not need\n'
+ ' encoded-word <t...@example.com>\n'),
+ ('"A véry long name with, comma" <t...@example.com>',
+ # (This isn't the best fold point, but it's not invalid.)
+ 'A =?utf-8?q?v=C3=A9ry_long_name_with?=\n'
+ ' =?utf-8?q?=2C?= comma <t...@example.com>\n'),
+ ('"A véry long name containing a, comma" <t...@example.com>',
+ 'A =?utf-8?q?v=C3=A9ry?= long name\n'
+ ' containing =?utf-8?q?a=2C?= comma\n'
+ ' <t...@example.com>\n'),
+ ]
+ for (to, folded) in cases:
+ with self.subTest(to=to):
+ self._test(parser.get_address_list(to)[0], folded,
policy=policy)
+
def test_address_list_with_list_separator_after_fold(self):
a = 'x' * 66 + '@example.com'
to = f'{a}, "Hübsch Kaktus" <beauti...@example.com>'
diff --git
a/Misc/NEWS.d/next/Security/2024-08-06-12-27-34.gh-issue-121284.8rwPxe.rst
b/Misc/NEWS.d/next/Security/2024-08-06-12-27-34.gh-issue-121284.8rwPxe.rst
new file mode 100644
index 00000000000000..923e91170d355f
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2024-08-06-12-27-34.gh-issue-121284.8rwPxe.rst
@@ -0,0 +1,7 @@
+Fix bug in the folding of rfc2047 encoded-words when flattening an email
message
+using a modern email policy. Previously when an encoded-word was too long
+for a line, it would be decoded, split across lines, and re-encoded. But commas
+and other special characters in the original text could be left unencoded and
+unquoted. This could theoretically be used to spoof header lines using
+a carefully constructed encoded-word if the resulting rendered email was
+transmitted or re-parsed.
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