From 1703bdda0ffc08f7035a8db5368d9eb448a910d2 Mon Sep 17 00:00:00 2001
From: Seth Michael Larson <seth@python.org>
Date: Fri, 20 Mar 2026 09:30:02 -0500
Subject: [PATCH 1/4] gh-146211: Reject CR/LF in HTTP tunnel request headers

---
 Lib/http/client.py                                                       |   21 ++++
 Lib/test/test_httplib.py                                                 |   45 ++++++++++
 Misc/NEWS.d/next/Security/2026-03-20-09-29-42.gh-issue-146211.PQVbs7.rst |    2 
 3 files changed, 65 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Security/2026-03-20-09-29-42.gh-issue-146211.PQVbs7.rst

Index: Python-3.6.15/Lib/http/client.py
===================================================================
--- Python-3.6.15.orig/Lib/http/client.py	2026-04-27 12:25:19.586019639 +0200
+++ Python-3.6.15/Lib/http/client.py	2026-04-27 12:59:20.667442356 +0200
@@ -936,14 +936,29 @@
         self.debuglevel = level
 
     def _tunnel(self):
+        if _contains_disallowed_url_pchar_re.search(self._tunnel_host):
+            raise ValueError('Tunnel host can\'t contain control characters %r'
+                             % (self._tunnel_host,))
         connect_str = "CONNECT %s:%d HTTP/1.0\r\n" % (self._tunnel_host,
             self._tunnel_port)
         connect_bytes = connect_str.encode("ascii")
         self.send(connect_bytes)
         for header, value in self._tunnel_headers.items():
-            header_str = "%s: %s\r\n" % (header, value)
-            header_bytes = header_str.encode("latin-1")
-            self.send(header_bytes)
+            if hasattr(header, 'encode'):
+                header = header.encode('ascii')
+
+            if not _is_legal_header_name(header):
+                raise ValueError('Invalid header name %r' % (header,))
+
+            if hasattr(value, 'encode'):
+                value = value.encode('latin-1')
+            elif isinstance(value, int):
+                value = str(value).encode('ascii')
+
+            if _is_illegal_header_value(value):
+                raise ValueError('Invalid header value %r' % (value,))
+
+            self.send(header + b': ' + value + b'\r\n')
         self.send(b'\r\n')
 
         response = self.response_class(self.sock, method=self._method)
Index: Python-3.6.15/Lib/test/test_httplib.py
===================================================================
--- Python-3.6.15.orig/Lib/test/test_httplib.py	2026-04-27 12:25:19.586571228 +0200
+++ Python-3.6.15/Lib/test/test_httplib.py	2026-04-27 12:25:19.819108968 +0200
@@ -344,6 +344,51 @@
                 with self.assertRaisesRegex(ValueError, 'Invalid header'):
                     conn.putheader(name, value)
 
+    def test_invalid_tunnel_headers(self):
+        cases = (
+            ('Invalid\r\nName', 'ValidValue'),
+            ('Invalid\rName', 'ValidValue'),
+            ('Invalid\nName', 'ValidValue'),
+            ('\r\nInvalidName', 'ValidValue'),
+            ('\rInvalidName', 'ValidValue'),
+            ('\nInvalidName', 'ValidValue'),
+            (' InvalidName', 'ValidValue'),
+            ('\tInvalidName', 'ValidValue'),
+            ('Invalid:Name', 'ValidValue'),
+            (':InvalidName', 'ValidValue'),
+            ('ValidName', 'Invalid\r\nValue'),
+            ('ValidName', 'Invalid\rValue'),
+            ('ValidName', 'Invalid\nValue'),
+            ('ValidName', 'InvalidValue\r\n'),
+            ('ValidName', 'InvalidValue\r'),
+            ('ValidName', 'InvalidValue\n'),
+        )
+        for name, value in cases:
+            with self.subTest((name, value)):
+                conn = client.HTTPConnection('example.com')
+                conn.set_tunnel('tunnel', headers={
+                    name: value
+                })
+                conn.sock = FakeSocket('')
+                with self.assertRaisesRegex(ValueError, 'Invalid header'):
+                    conn._tunnel()  # Called in .connect()
+
+    def test_invalid_tunnel_host(self):
+        cases = (
+            'invalid\r.host',
+            '\ninvalid.host',
+            'invalid.host\r\n',
+            'invalid.host\x00',
+            'invalid host',
+        )
+        for tunnel_host in cases:
+            with self.subTest(tunnel_host):
+                conn = client.HTTPConnection('example.com')
+                conn.set_tunnel(tunnel_host)
+                conn.sock = FakeSocket('')
+                with self.assertRaisesRegex(ValueError, 'Tunnel host can\'t contain control characters'):
+                    conn._tunnel()  # Called in .connect()
+
     def test_headers_debuglevel(self):
         body = (
             b'HTTP/1.1 200 OK\r\n'
Index: Python-3.6.15/Misc/NEWS.d/next/Security/2026-03-20-09-29-42.gh-issue-146211.PQVbs7.rst
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ Python-3.6.15/Misc/NEWS.d/next/Security/2026-03-20-09-29-42.gh-issue-146211.PQVbs7.rst	2026-04-27 12:25:19.819667349 +0200
@@ -0,0 +1,2 @@
+Reject CR/LF characters in tunnel request headers for the
+HTTPConnection.set_tunnel() method.