bpo-39603: Prevent header injection in http methods (GH-18485)

reject control chars in http method in http.client.putrequest to prevent http header injection

1 files changed, 15 insertions, 0 deletions

diff --git a/Lib/http/client.py b/Lib/http/client.py
index 500230d..15abcfe 100644
--- a/Lib/http/client.py
+++ b/Lib/http/client.py
@@ -147,6 +147,10 @@ _contains_disallowed_url_pchar_re = re.compile('[\x00-\x20\x7f]')
 #  _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'}
@@ -1102,6 +1106,8 @@ class HTTPConnection:
         else:
             raise CannotSendRequest(self.__state)
 
+        self._validate_method(method)
+
         # Save the method for use later in the response phase
         self._method = method
 
@@ -1192,6 +1198,15 @@ class HTTPConnection:
         # 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.