python
diff --git a/‎Lib/http/client.py
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+15Lines changed: 15 additions & 0 deletions b/‎Lib/http/client.py
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diff --git a/‎Lib/test/test_httplib.py
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+22Lines changed: 22 additions & 0 deletions b/‎Lib/test/test_httplib.py
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diff --git a/‎Misc/NEWS.d/next/Security/2020-02-12-14-17-39.bpo-39603.Gt3RSg.rst
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@@ -151,6 +151,10 @@
 #  _is_allowed_url_pchars_re = re.compile(r"^[/!$&'()*+,;=:@%a-zA-Z0-9._~-]+$")
 # We are more lenient for assumed real world compatibility purposes.
 
+# These characters are not allowed within HTTP method names
+# to prevent http header injection.
+_contains_disallowed_method_pchar_re = re.compile('[\x00-\x1f]')
+
 # We always set the Content-Length header for these methods because some
 # servers will otherwise respond with a 411
 _METHODS_EXPECTING_BODY = {'PATCH', 'POST', 'PUT'}
@@ -1119,6 +1123,8 @@ def putrequest(self, method, url, skip_host=False,
         else:
             raise CannotSendRequest(self.__state)
 
+        self._validate_method(method)
+
         # Save the method for use later in the response phase
         self._method = method
 
@@ -1209,6 +1215,15 @@ def _encode_request(self, request):
         # ASCII also helps prevent CVE-2019-9740.
         return request.encode('ascii')
 
+    def _validate_method(self, method):
+        """Validate a method name for putrequest."""
+        # prevent http header injection
+        match = _contains_disallowed_method_pchar_re.search(method)
+        if match:
+            raise ValueError(
+                    f"method can't contain control characters. {method!r} "
+                    f"(found at least {match.group()!r})")
+
     def _validate_path(self, url):
         """Validate a url for putrequest."""
         # Prevent CVE-2019-9740.
 
@@ -359,6 +359,28 @@ def test_headers_debuglevel(self):
         self.assertEqual(lines[2], "header: Second: val")
 
 
+class HttpMethodTests(TestCase):
+    def test_invalid_method_names(self):
+        methods = (
+            'GET\r',
+            'POST\n',
+            'PUT\n\r',
+            'POST\nValue',
+            'POST\nHOST:abc',
+            'GET\nrHost:abc\n',
+            'POST\rRemainder:\r',
+            'GET\rHOST:\n',
+            '\nPUT'
+        )
+
+        for method in methods:
+            with self.assertRaisesRegex(
+                    ValueError, "method can't contain control characters"):
+                conn = client.HTTPConnection('example.com')
+                conn.sock = FakeSocket(None)
+                conn.request(method=method, url="/")
+
+
 class TransferEncodingTest(TestCase):
     expected_body = b"It's just a flesh wound"
 
 
@@ -0,0 +1,2 @@
+Prevent http header injection by rejecting control characters in
+http.client.putrequest(...).
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+Prevent http header injection by rejecting control characters in`
	`2`	`+http.client.putrequest(...).`