Check 'Host' header for local connections

Author: takluyver

notebook/base/handlers.py

@@ -5,6 +5,7 @@
 
 import datetime
 import functools
+import ipaddress
 import json
 import mimetypes
 import os
@@ -411,6 +412,39 @@ def check_xsrf_cookie(self):
             return
         return super(IPythonHandler, self).check_xsrf_cookie()
 
+    def check_host(self):
+        """Check the host header if remote access disallowed.
+
+        Returns True if the request should continue, False otherwise.
+        """
+        if self.settings.get('allow_remote_access', False):
+            return True
+
+        # Remove port (e.g. ':8888') from host
+        host = re.match(r'^(.*?)(:\d+)?$', self.request.host).group(1)
+
+        # Browsers format IPv6 addresses like [::1]; we need to remove the []
+        if host.startswith('[') and host.endswith(']'):
+            host = host[1:-1]
+
+        try:
+            addr = ipaddress.ip_address(host)
+        except ValueError:
+            # Not an IP address: check against hostnames
+            allow = host in self.settings.get('local_hostnames', [])
+        else:
+            allow = addr.is_loopback
+
+        if not allow:
+            self.log.warning("Blocking request with non-local 'Host' %s (%s)",
+                             host, self.request.host)
+        return allow
+
+    def prepare(self):
+        if not self.check_host():
+            raise web.HTTPError(403)
+        return super(IPythonHandler, self).prepare()
+
     #---------------------------------------------------------------
     # template rendering
     #---------------------------------------------------------------

notebook/notebookapp.py

@@ -252,6 +252,8 @@ def init_settings(self, jupyter_app, kernel_manager, contents_manager,
             password=jupyter_app.password,
             xsrf_cookies=True,
             disable_check_xsrf=jupyter_app.disable_check_xsrf,
+            allow_remote_access=jupyter_app.allow_remote_access,
+            local_hostnames=jupyter_app.local_hostnames,
 
             # managers
             kernel_manager=kernel_manager,
@@ -831,6 +833,29 @@ def _token_changed(self, change):
         """
     )
 
+    allow_remote_access = Bool(False, config=True,
+       help="""Allow requests where the Host header doesn't point to a local server
+
+       By default, requests get a 403 forbidden response if the 'Host' header
+       shows that the browser thinks it's on a non-local domain.
+       Setting this option to True disables this check.
+
+       This protects against 'DNS rebinding' attacks, where a remote web server
+       serves you a page and then changes its DNS to send later requests to a
+       local IP, bypassing same-origin checks.
+
+       Local IP addresses (such as 127.0.0.1 and ::1) are allowed as local,
+       along with hostnames configured in local_hostnames.
+       """)
+
+    local_hostnames = List(Unicode(), ['localhost'], config=True,
+       help="""Hostnames to allow as local when allow_remote_access is False.
+
+       Local IP addresses (such as 127.0.0.1 and ::1) are automatically accepted
+       as local as well.
+       """
+    )
+
     open_browser = Bool(True, config=True,
                         help="""Whether to open in a browser after starting.
                         The specific browser used is platform dependent and

setup.py

@@ -94,6 +94,7 @@
         'prometheus_client'
     ],
     extras_require = {
+        ':python_version == "2.7"': ['ipaddress'],
         'test:python_version == "2.7"': ['mock'],
         'test': ['nose', 'coverage', 'requests', 'nose_warnings_filters',
                  'nbval', 'nose-exclude'],