From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Seth Michael Larson <seth@python.org>
Date: Tue, 20 Jan 2026 14:46:32 -0600
Subject: 00475: CVE-2025-15367

gh-143923: Reject control characters in POP3 commands

(cherry-picked from commit b234a2b67539f787e191d2ef19a7cbdce32874e7)
---
 Lib/poplib.py                                             | 2 ++
 Lib/test/test_poplib.py                                   | 8 ++++++++
 .../2026-01-16-11-43-47.gh-issue-143923.DuytMe.rst        | 1 +
 3 files changed, 11 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Security/2026-01-16-11-43-47.gh-issue-143923.DuytMe.rst

diff --git a/Lib/poplib.py b/Lib/poplib.py
index 9796f0d2f9..64690628fe 100644
--- a/Lib/poplib.py
+++ b/Lib/poplib.py
@@ -117,6 +117,8 @@ class POP3:
     def _putcmd(self, line):
         if self._debugging: print('*cmd*', repr(line))
         line = bytes(line, self.encoding)
+        if re.search(b'[\x00-\x1F\x7F]', line):
+            raise ValueError('Control characters not allowed in commands')
         self._putline(line)
 
 
diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py
index 234c855545..18b8c191ab 100644
--- a/Lib/test/test_poplib.py
+++ b/Lib/test/test_poplib.py
@@ -12,6 +12,7 @@ import errno
 
 from unittest import TestCase, skipUnless
 from test import support as test_support
+from test.support import control_characters_c0
 threading = test_support.import_module('threading')
 
 HOST = test_support.HOST
@@ -349,6 +350,13 @@ class TestPOP3Class(TestCase):
         self.assertIsNone(self.client.sock)
         self.assertIsNone(self.client.file)
 
+    def test_control_characters(self):
+        for c0 in control_characters_c0():
+            with self.assertRaises(ValueError):
+                self.client.user(f'user{c0}')
+            with self.assertRaises(ValueError):
+                self.client.pass_(f'{c0}pass')
+
     @requires_ssl
     def test_stls_capa(self):
         capa = self.client.capa()
diff --git a/Misc/NEWS.d/next/Security/2026-01-16-11-43-47.gh-issue-143923.DuytMe.rst b/Misc/NEWS.d/next/Security/2026-01-16-11-43-47.gh-issue-143923.DuytMe.rst
new file mode 100644
index 0000000000..3cde4df3e0
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2026-01-16-11-43-47.gh-issue-143923.DuytMe.rst
@@ -0,0 +1 @@
+Reject control characters in POP3 commands.