Stripped headers containing underscores to prevent spoofing in WSGI environ.

This is a security fix. Disclosure following shortly.

Thanks to Jedediah Smith for the report.

tests/servers/test_basehttp.py

@@ -6,6 +6,11 @@ from django.test.utils import captured_stderr
 from django.utils.six import BytesIO
 
 
+class Stub(object):
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+
 class WSGIRequestHandlerTestCase(TestCase):
     def test_https(self):
         request = WSGIRequest(RequestFactory().get('/').environ)
@@ -20,3 +25,53 @@ class WSGIRequestHandlerTestCase(TestCase):
                 "but it only supports HTTP.",
                 stderr.getvalue()
             )
+
+    def test_strips_underscore_headers(self):
+        """WSGIRequestHandler ignores headers containing underscores.
+
+        This follows the lead of nginx and Apache 2.4, and is to avoid
+        ambiguity between dashes and underscores in mapping to WSGI environ,
+        which can have security implications.
+        """
+        def test_app(environ, start_response):
+            """A WSGI app that just reflects its HTTP environ."""
+            start_response('200 OK', [])
+            http_environ_items = sorted(
+                '%s:%s' % (k, v) for k, v in environ.items()
+                if k.startswith('HTTP_')
+            )
+            yield (','.join(http_environ_items)).encode('utf-8')
+
+        rfile = BytesIO()
+        rfile.write(b"GET / HTTP/1.0\r\n")
+        rfile.write(b"Some-Header: good\r\n")
+        rfile.write(b"Some_Header: bad\r\n")
+        rfile.write(b"Other_Header: bad\r\n")
+        rfile.seek(0)
+
+        # WSGIRequestHandler closes the output file; we need to make this a
+        # no-op so we can still read its contents.
+        class UnclosableBytesIO(BytesIO):
+            def close(self):
+                pass
+
+        wfile = UnclosableBytesIO()
+
+        def makefile(mode, *a, **kw):
+            if mode == 'rb':
+                return rfile
+            elif mode == 'wb':
+                return wfile
+
+        request = Stub(makefile=makefile)
+        server = Stub(base_environ={}, get_app=lambda: test_app)
+
+        # We don't need to check stderr, but we don't want it in test output
+        with captured_stderr():
+            # instantiating a handler runs the request as side effect
+            WSGIRequestHandler(request, '192.168.0.2', server)
+
+        wfile.seek(0)
+        body = list(wfile.readlines())[-1]
+
+        self.assertEqual(body, b'HTTP_SOME_HEADER:good')