From 7485ee5e2cf81d3e5ad0d9c3be73cecd2ab4eec7 Mon Sep 17 00:00:00 2001
From: Seth Michael Larson <seth@python.org>
Date: Fri, 16 Jan 2026 10:54:09 -0600
Subject: [PATCH 1/2] Add 'test.support' fixture for C0 control characters

---
 Lib/imaplib.py                                                           |    4 +++-
 Lib/test/test_imaplib.py                                                 |    6 ++++++
 Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst |    1 +
 3 files changed, 10 insertions(+), 1 deletion(-)

Index: Python-3.10.19/Lib/imaplib.py
===================================================================
--- Python-3.10.19.orig/Lib/imaplib.py	2026-02-12 01:05:53.821319313 +0100
+++ Python-3.10.19/Lib/imaplib.py	2026-02-12 01:06:28.558652908 +0100
@@ -132,7 +132,7 @@
 # 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:
@@ -994,6 +994,8 @@
             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
Index: Python-3.10.19/Lib/test/test_imaplib.py
===================================================================
--- Python-3.10.19.orig/Lib/test/test_imaplib.py	2026-02-12 01:05:55.293033311 +0100
+++ Python-3.10.19/Lib/test/test_imaplib.py	2026-02-12 01:07:45.387053336 +0100
@@ -538,6 +538,12 @@
         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')
+
 
 class NewIMAPTests(NewIMAPTestsMixin, unittest.TestCase):
     imap_class = imaplib.IMAP4
Index: Python-3.10.19/Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ Python-3.10.19/Misc/NEWS.d/next/Security/2026-01-16-11-41-06.gh-issue-143921.AeCOor.rst	2026-02-12 01:06:28.559224837 +0100
@@ -0,0 +1 @@
+Reject control characters in IMAP commands.