File CVE-2025-11468-email-hdr-fold-comment.patch of Package python314
From df45bd1aafc3b6792d43661207d2b7eb3a14d214 Mon Sep 17 00:00:00 2001
From: Seth Michael Larson <seth@python.org>
Date: Mon, 19 Jan 2026 06:38:22 -0600
Subject: [PATCH] gh-143935: Email preserve parens when folding comments
(GH-143936)
Fix a bug in the folding of comments when flattening an email message
using a modern email policy. Comments consisting of a very long sequence of
non-foldable characters could trigger a forced line wrap that omitted the
required leading space on the continuation line, causing the remainder of
the comment to be interpreted as a new header field. This enabled header
injection with carefully crafted inputs.
(cherry picked from commit 17d1490aa97bd6b98a42b1a9b324ead84e7fd8a2)
Co-authored-by: Seth Michael Larson <seth@python.org>
Co-authored-by: Denis Ledoux <dle@odoo.com>
---
Lib/email/_header_value_parser.py | 15 +++++++++++-
.../test_email/test__header_value_parser.py | 23 +++++++++++++++++++
...-01-16-14-40-31.gh-issue-143935.U2YtKl.rst | 6 +++++
3 files changed, 43 insertions(+), 1 deletion(-)
create mode 100644 Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst
diff --git a/Lib/email/_header_value_parser.py b/Lib/email/_header_value_parser.py
index 68c2cf9585c5b4..51727688c059ed 100644
--- a/Lib/email/_header_value_parser.py
+++ b/Lib/email/_header_value_parser.py
@@ -101,6 +101,12 @@ def make_quoted_pairs(value):
return str(value).replace('\\', '\\\\').replace('"', '\\"')
+def make_parenthesis_pairs(value):
+ """Escape parenthesis and backslash for use within a comment."""
+ return str(value).replace('\\', '\\\\') \
+ .replace('(', '\\(').replace(')', '\\)')
+
+
def quote_string(value):
escaped = make_quoted_pairs(value)
return f'"{escaped}"'
@@ -939,7 +945,7 @@ def value(self):
return ' '
def startswith_fws(self):
- return True
+ return self and self[0] in WSP
class ValueTerminal(Terminal):
@@ -2959,6 +2965,13 @@ def _refold_parse_tree(parse_tree, *, policy):
[ValueTerminal(make_quoted_pairs(p), 'ptext')
for p in newparts] +
[ValueTerminal('"', 'ptext')])
+ if part.token_type == 'comment':
+ newparts = (
+ [ValueTerminal('(', 'ptext')] +
+ [ValueTerminal(make_parenthesis_pairs(p), 'ptext')
+ if p.token_type == 'ptext' else p
+ for p in newparts] +
+ [ValueTerminal(')', 'ptext')])
if not part.as_ew_allowed:
wrap_as_ew_blocked += 1
newparts.append(end_ew_not_allowed)
diff --git a/Lib/test/test_email/test__header_value_parser.py b/Lib/test/test_email/test__header_value_parser.py
index 426ec4644e3096..e28fe3892015b9 100644
--- a/Lib/test/test_email/test__header_value_parser.py
+++ b/Lib/test/test_email/test__header_value_parser.py
@@ -3294,6 +3294,29 @@ def test_address_list_with_specials_in_long_quoted_string(self):
with self.subTest(to=to):
self._test(parser.get_address_list(to)[0], folded, policy=policy)
+ def test_address_list_with_long_unwrapable_comment(self):
+ policy = self.policy.clone(max_line_length=40)
+ cases = [
+ # (to, folded)
+ ('(loremipsumdolorsitametconsecteturadipi)<spy@example.org>',
+ '(loremipsumdolorsitametconsecteturadipi)<spy@example.org>\n'),
+ ('<spy@example.org>(loremipsumdolorsitametconsecteturadipi)',
+ '<spy@example.org>(loremipsumdolorsitametconsecteturadipi)\n'),
+ ('(loremipsum dolorsitametconsecteturadipi)<spy@example.org>',
+ '(loremipsum dolorsitametconsecteturadipi)<spy@example.org>\n'),
+ ('<spy@example.org>(loremipsum dolorsitametconsecteturadipi)',
+ '<spy@example.org>(loremipsum\n dolorsitametconsecteturadipi)\n'),
+ ('(Escaped \\( \\) chars \\\\ in comments stay escaped)<spy@example.org>',
+ '(Escaped \\( \\) chars \\\\ in comments stay\n escaped)<spy@example.org>\n'),
+ ('((loremipsum)(loremipsum)(loremipsum)(loremipsum))<spy@example.org>',
+ '((loremipsum)(loremipsum)(loremipsum)(loremipsum))<spy@example.org>\n'),
+ ('((loremipsum)(loremipsum)(loremipsum) (loremipsum))<spy@example.org>',
+ '((loremipsum)(loremipsum)(loremipsum)\n (loremipsum))<spy@example.org>\n'),
+ ]
+ for (to, folded) in cases:
+ with self.subTest(to=to):
+ self._test(parser.get_address_list(to)[0], folded, policy=policy)
+
# XXX Need tests with comments on various sides of a unicode token,
# and with unicode tokens in the comments. Spaces inside the quotes
# currently don't do the right thing.
diff --git a/Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst b/Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst
new file mode 100644
index 00000000000000..c3d864936884ac
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-01-16-14-40-31.gh-issue-143935.U2YtKl.rst
@@ -0,0 +1,6 @@
+Fixed a bug in the folding of comments when flattening an email message
+using a modern email policy. Comments consisting of a very long sequence of
+non-foldable characters could trigger a forced line wrap that omitted the
+required leading space on the continuation line, causing the remainder of
+the comment to be interpreted as a new header field. This enabled header
+injection with carefully crafted inputs.
