check and test for headers containing return characters or leading whitespace

AUTHORS.rst

@@ -166,3 +166,4 @@ Patches and Suggestions
 - Dmitry Dygalo (`@Stranger6667 <https://github.com/Stranger6667>`_)
 - piotrjurkiewicz
 - Jesse Shapiro <jesse@jesseshapiro.net> (`@haikuginger <https://github.com/haikuginger>`_)
+- Nate Prewitt <nate.prewitt@gmail.com> (`@nateprewitt <https://github.com/nateprewitt>`_)

requests/exceptions.py

@@ -80,7 +80,11 @@ class InvalidSchema(RequestException, ValueError):
 
 
 class InvalidURL(RequestException, ValueError):
-    """ The URL provided was somehow invalid. """
+    """The URL provided was somehow invalid."""
+
+
+class InvalidHeader(RequestException, ValueError):
+    """The header value provided was somehow invalid."""
 
 
 class ChunkedEncodingError(RequestException):

requests/models.py

@@ -27,7 +27,8 @@ from .exceptions import (
 from .utils import (
     guess_filename, get_auth_from_url, requote_uri,
     stream_decode_response_unicode, to_key_val_list, parse_header_links,
-    iter_slices, guess_json_utf, super_len, to_native_string)
+    iter_slices, guess_json_utf, super_len, to_native_string, 
+    check_header_validity)
 from .compat import (
     cookielib, urlunparse, urlsplit, urlencode, str, bytes, StringIO,
     is_py2, chardet, builtin_str, basestring)
@@ -403,10 +404,13 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
     def prepare_headers(self, headers):
         """Prepares the given HTTP headers."""
 
+        self.headers = CaseInsensitiveDict()
         if headers:
-            self.headers = CaseInsensitiveDict((to_native_string(name), value) for name, value in headers.items())
-        else:
-            self.headers = CaseInsensitiveDict()
+            for header in headers.items():
+                # Raise exception on invalid header value.
+                check_header_validity(header)
+                name, value = header
+                self.headers[to_native_string(name)] = value
 
     def prepare_body(self, data, files, json=None):
         """Prepares the given HTTP body data."""

requests/utils.py

@@ -27,7 +27,7 @@ from .compat import (quote, urlparse, bytes, str, OrderedDict, unquote, is_py2,
                      basestring)
 from .cookies import RequestsCookieJar, cookiejar_from_dict
 from .structures import CaseInsensitiveDict
-from .exceptions import InvalidURL, FileModeWarning
+from .exceptions import InvalidURL, InvalidHeader, FileModeWarning
 
 _hush_pyflakes = (RequestsCookieJar,)
 
@@ -732,6 +732,24 @@ def to_native_string(string, encoding='ascii'):
 
     return out
 
+# Moved outside of function to avoid recompile every call
+_CLEAN_HEADER_REGEX_BYTE = re.compile(b'^\\S[^\\r\\n]*$|^$')
+_CLEAN_HEADER_REGEX_STR = re.compile(r'^\S[^\r\n]*$|^$')
+
+def check_header_validity(header):
+    """Verifies that header value doesn't contain leading whitespace or
+    return characters. This prevents unintended header injection.
+
+    :param header: tuple, in the format (name, value).
+    """
+    name, value = header
+
+    if isinstance(value, bytes):
+        pat = _CLEAN_HEADER_REGEX_BYTE
+    else:
+        pat = _CLEAN_HEADER_REGEX_STR
+    if not pat.match(value):
+        raise InvalidHeader("Invalid return character or leading space in header: %s" % name)
 
 def urldefragauth(url):
     """

tests/test_requests.py

@@ -23,7 +23,7 @@ from requests.cookies import cookiejar_from_dict, morsel_to_cookie
 from requests.exceptions import (
     ConnectionError, ConnectTimeout, InvalidSchema, InvalidURL,
     MissingSchema, ReadTimeout, Timeout, RetryError, TooManyRedirects,
-    ProxyError)
+    ProxyError, InvalidHeader)
 from requests.models import PreparedRequest
 from requests.structures import CaseInsensitiveDict
 from requests.sessions import SessionRedirectMixin
@@ -1128,6 +1128,47 @@ class TestRequests:
         assert 'unicode' in p.headers.keys()
         assert 'byte' in p.headers.keys()
 
+    def test_header_validation(self,httpbin):
+        """Ensure prepare_headers regex isn't flagging valid header contents."""
+        headers_ok = {'foo': 'bar baz qux',
+                      'bar': '1',
+                      'baz': '',
+                      'qux': str.encode(u'fbbq')}
+        r = requests.get(httpbin('get'), headers=headers_ok)
+        assert r.request.headers['foo'] == headers_ok['foo']
+
+    def test_header_no_return_chars(self, httpbin):
+        """Ensure that a header containing return character sequences raise an
+        exception. Otherwise, multiple headers are created from single string.
+        """
+        headers_ret = {'foo': 'bar\r\nbaz: qux'}
+        headers_lf = {'foo': 'bar\nbaz: qux'}
+        headers_cr = {'foo': 'bar\rbaz: qux'}
+
+        # Test for newline
+        with pytest.raises(InvalidHeader):
+            r = requests.get(httpbin('get'), headers=headers_ret)
+        # Test for line feed
+        with pytest.raises(InvalidHeader):
+            r = requests.get(httpbin('get'), headers=headers_lf)
+        # Test for carriage return
+        with pytest.raises(InvalidHeader):
+            r = requests.get(httpbin('get'), headers=headers_cr)
+
+    def test_header_no_leading_space(self, httpbin):
+        """Ensure headers containing leading whitespace raise
+        InvalidHeader Error before sending.
+        """
+        headers_space = {'foo': ' bar'}
+        headers_tab = {'foo': '   bar'}
+
+        # Test for whitespace
+        with pytest.raises(InvalidHeader):
+            r = requests.get(httpbin('get'), headers=headers_space)
+        # Test for tab
+        with pytest.raises(InvalidHeader):
+            r = requests.get(httpbin('get'), headers=headers_tab)
+
     @pytest.mark.parametrize('files', ('foo', b'foo', bytearray(b'foo')))
     def test_can_send_objects_with_files(self, httpbin, files):
         data = {'a': 'this is a string'}