check Referer on API requests

For CSRF

jupyterhub/apihandlers/base.py

@@ -9,8 +9,43 @@ from http.client import responses
 from tornado import web
 
 from ..handlers import BaseHandler
+from ..utils import url_path_join
 
 class APIHandler(BaseHandler):
+
+    def check_referer(self):
+        """Check Origin for cross-site API requests.
+        
+        Copied from WebSocket with changes:
+        
+        - allow unspecified host/referer (e.g. scripts)
+        """
+        host = self.request.headers.get("Host")
+        referer = self.request.headers.get("Referer")
+
+        # If no header is provided, assume it comes from a script/curl.
+        # We are only concerned with cross-site browser stuff here.
+        if not host:
+            self.log.warn("Blocking API request with no host")
+            return False
+        if not referer:
+            self.log.warn("Blocking API request with no referer")
+            return False
+        
+        host_path = url_path_join(host, self.hub.server.base_url)
+        referer_path = referer.split('://', 1)[-1]
+        if not (referer_path + '/').startswith(host_path):
+            self.log.warn("Blocking Cross Origin API request.  Referer: %s, Host: %s",
+                referer, host_path)
+            return False
+        return True
+    
+    def get_current_user_cookie(self):
+        """Override get_user_cookie to check Referer header"""
+        if not self.check_referer():
+            return None
+        return super().get_current_user_cookie()
+
     def get_json_body(self):
         """Return the body of the request as JSON data."""
         if not self.request.body:
@@ -23,7 +58,6 @@ class APIHandler(BaseHandler):
             self.log.error("Couldn't parse JSON", exc_info=True)
             raise web.HTTPError(400, 'Invalid JSON in body of request')
         return model
-        
     
     def write_error(self, status_code, **kwargs):
         """Write JSON errors instead of HTML"""

jupyterhub/tests/test_api.py

@@ -4,6 +4,7 @@ import json
 import time
 from datetime import timedelta
 from queue import Queue
+from urllib.parse import urlparse
 
 import requests
 
@@ -97,6 +98,51 @@ def test_auth_api(app):
     )
     assert r.status_code == 403
 
+
+def test_referer_check(app, io_loop):
+    url = app.hub.server.url
+    host = urlparse(url).netloc
+    user = find_user(app.db, 'admin')
+    if user is None:
+        user = add_user(app.db, name='admin', admin=True)
+    cookies = app.login_user('admin')
+    app_user = get_app_user(app, 'admin')
+    # stop the admin's server so we don't mess up future tests
+    io_loop.run_sync(lambda : app.proxy.delete_user(app_user))
+    io_loop.run_sync(app_user.stop)
+    
+    r = api_request(app, 'users',
+        headers={
+            'Authorization': '',
+            'Referer': 'null',
+        }, cookies=cookies,
+    )
+    assert r.status_code == 403
+    r = api_request(app, 'users',
+        headers={
+            'Authorization': '',
+            'Referer': 'http://attack.com/csrf/vulnerability',
+        }, cookies=cookies,
+    )
+    assert r.status_code == 403
+    r = api_request(app, 'users',
+        headers={
+            'Authorization': '',
+            'Referer': url,
+            'Host': host,
+        }, cookies=cookies,
+    )
+    assert r.status_code == 200
+    r = api_request(app, 'users',
+        headers={
+            'Authorization': '',
+            'Referer': ujoin(url, 'foo/bar/baz/bat'),
+            'Host': host,
+        }, cookies=cookies,
+    )
+    assert r.status_code == 200
+
+
 def test_get_users(app):
     db = app.db
     r = api_request(app, 'users')