forked from pool/python313
Matěj Cepl
79a850acd8
Preserving parens when folding comments in email headers (bsc#1257029, CVE-2025-11468).
109 lines
5.6 KiB
Diff
109 lines
5.6 KiB
Diff
From 636f0b674ac4f4778b3ba32e950fdfc58a54b9e1 Mon Sep 17 00:00:00 2001
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From: Seth Michael Larson <seth@python.org>
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Date: Mon, 19 Jan 2026 06:38:22 -0600
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Subject: [PATCH] gh-143935: Email preserve parens when folding comments
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(GH-143936)
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Fix a bug in the folding of comments when flattening an email message
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using a modern email policy. Comments consisting of a very long sequence of
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non-foldable characters could trigger a forced line wrap that omitted the
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required leading space on the continuation line, causing the remainder of
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the comment to be interpreted as a new header field. This enabled header
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injection with carefully crafted inputs.
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(cherry picked from commit 17d1490aa97bd6b98a42b1a9b324ead84e7fd8a2)
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Co-authored-by: Seth Michael Larson <seth@python.org>
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Co-authored-by: Denis Ledoux <dle@odoo.com>
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---
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Lib/email/_header_value_parser.py | 15 ++++++
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Lib/test/test_email/test__header_value_parser.py | 23 ++++++++++
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Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst | 6 ++
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3 files changed, 43 insertions(+), 1 deletion(-)
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create mode 100644 Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst
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Index: Python-3.13.11/Lib/email/_header_value_parser.py
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===================================================================
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--- Python-3.13.11.orig/Lib/email/_header_value_parser.py 2025-12-05 17:06:33.000000000 +0100
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+++ Python-3.13.11/Lib/email/_header_value_parser.py 2026-01-29 19:25:21.986346350 +0100
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@@ -101,6 +101,12 @@
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return str(value).replace('\\', '\\\\').replace('"', '\\"')
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+def make_parenthesis_pairs(value):
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+ """Escape parenthesis and backslash for use within a comment."""
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+ return str(value).replace('\\', '\\\\') \
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+ .replace('(', '\\(').replace(')', '\\)')
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+
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+
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def quote_string(value):
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escaped = make_quoted_pairs(value)
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return f'"{escaped}"'
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@@ -933,7 +939,7 @@
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return ' '
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def startswith_fws(self):
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- return True
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+ return self and self[0] in WSP
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class ValueTerminal(Terminal):
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@@ -2924,6 +2930,13 @@
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[ValueTerminal(make_quoted_pairs(p), 'ptext')
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for p in newparts] +
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[ValueTerminal('"', 'ptext')])
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+ if part.token_type == 'comment':
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+ newparts = (
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+ [ValueTerminal('(', 'ptext')] +
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+ [ValueTerminal(make_parenthesis_pairs(p), 'ptext')
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+ if p.token_type == 'ptext' else p
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+ for p in newparts] +
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+ [ValueTerminal(')', 'ptext')])
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if not part.as_ew_allowed:
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wrap_as_ew_blocked += 1
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newparts.append(end_ew_not_allowed)
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Index: Python-3.13.11/Lib/test/test_email/test__header_value_parser.py
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===================================================================
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--- Python-3.13.11.orig/Lib/test/test_email/test__header_value_parser.py 2025-12-05 17:06:33.000000000 +0100
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+++ Python-3.13.11/Lib/test/test_email/test__header_value_parser.py 2026-01-29 19:25:21.986906275 +0100
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@@ -3219,6 +3219,29 @@
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with self.subTest(to=to):
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self._test(parser.get_address_list(to)[0], folded, policy=policy)
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+ def test_address_list_with_long_unwrapable_comment(self):
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+ policy = self.policy.clone(max_line_length=40)
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+ cases = [
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+ # (to, folded)
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+ ('(loremipsumdolorsitametconsecteturadipi)<spy@example.org>',
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+ '(loremipsumdolorsitametconsecteturadipi)<spy@example.org>\n'),
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+ ('<spy@example.org>(loremipsumdolorsitametconsecteturadipi)',
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+ '<spy@example.org>(loremipsumdolorsitametconsecteturadipi)\n'),
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+ ('(loremipsum dolorsitametconsecteturadipi)<spy@example.org>',
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+ '(loremipsum dolorsitametconsecteturadipi)<spy@example.org>\n'),
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+ ('<spy@example.org>(loremipsum dolorsitametconsecteturadipi)',
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+ '<spy@example.org>(loremipsum\n dolorsitametconsecteturadipi)\n'),
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+ ('(Escaped \\( \\) chars \\\\ in comments stay escaped)<spy@example.org>',
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+ '(Escaped \\( \\) chars \\\\ in comments stay\n escaped)<spy@example.org>\n'),
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+ ('((loremipsum)(loremipsum)(loremipsum)(loremipsum))<spy@example.org>',
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+ '((loremipsum)(loremipsum)(loremipsum)(loremipsum))<spy@example.org>\n'),
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+ ('((loremipsum)(loremipsum)(loremipsum) (loremipsum))<spy@example.org>',
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+ '((loremipsum)(loremipsum)(loremipsum)\n (loremipsum))<spy@example.org>\n'),
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+ ]
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+ for (to, folded) in cases:
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+ with self.subTest(to=to):
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+ self._test(parser.get_address_list(to)[0], folded, policy=policy)
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+
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# XXX Need tests with comments on various sides of a unicode token,
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# and with unicode tokens in the comments. Spaces inside the quotes
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# currently don't do the right thing.
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Index: Python-3.13.11/Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst
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===================================================================
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--- /dev/null 1970-01-01 00:00:00.000000000 +0000
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+++ Python-3.13.11/Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst 2026-01-29 19:25:21.987305397 +0100
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@@ -0,0 +1,6 @@
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+Fixed a bug in the folding of comments when flattening an email message
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+using a modern email policy. Comments consisting of a very long sequence of
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+non-foldable characters could trigger a forced line wrap that omitted the
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+required leading space on the continuation line, causing the remainder of
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+the comment to be interpreted as a new header field. This enabled header
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+injection with carefully crafted inputs.
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