From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Seth Michael Larson <seth@python.org>
Date: Tue, 20 Jan 2026 14:45:42 -0600
Subject: 00474: CVE-2025-15366

Downstream only: Reject control characters in IMAP commands
---
 Lib/imaplib.py                                              | 4 +++-
 Lib/test/test_imaplib.py                                    | 6 ++++++
 .../Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst | 1 +
 3 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst

diff --git a/Lib/imaplib.py b/Lib/imaplib.py
index cbe129b3e7..b9c691aacd 100644
--- a/Lib/imaplib.py
+++ b/Lib/imaplib.py
@@ -131,7 +131,7 @@
 # We compile these in _mode_xxx.
 _Literal = br'.*{(?P<size>\d+)}$'
 _Untagged_status = br'\* (?P<data>\d+) (?P<type>[A-Z-]+)( (?P<data2>.*))?'
-
+_control_chars = re.compile(b'[\x00-\x1F\x7F]')
 
 
 class IMAP4:
@@ -1108,6 +1108,8 @@ def _command(self, name, *args):
             if arg is None: continue
             if isinstance(arg, str):
                 arg = bytes(arg, self._encoding)
+            if _control_chars.search(arg):
+                raise ValueError("Control characters not allowed in commands")
             data = data + b' ' + arg
 
         literal = self.literal
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index a03d7b8bb2..e26400b588 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -663,6 +663,12 @@ def test_unselect(self):
         self.assertEqual(data[0], b'Returned to authenticated state. (Success)')
         self.assertEqual(client.state, 'AUTH')
 
+    def test_control_characters(self):
+        client, _ = self._setup(SimpleIMAPHandler)
+        for c0 in support.control_characters_c0():
+            with self.assertRaises(ValueError):
+                client.login(f'user{c0}', 'pass')
+
     # property tests
 
     def test_file_property_should_not_be_accessed(self):
diff --git a/Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst b/Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst
new file mode 100644
index 0000000000..4e13fe92bc
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst
@@ -0,0 +1 @@
+Reject control characters in IMAP commands.