Fix open redirect

Make sure the "next" URL is in the same origin as Horizon before
redirecting to it.

Change-Id: I06b2bfc8e3638591615547780c3fa34b0abe19f6
Closes-bug: #1865026

horizon/test/unit/workflows/test_workflows.py

@@ -16,6 +16,7 @@ from unittest import mock
 
 from django import forms
 from django import http
+from django.test.utils import override_settings
 
 from horizon import base
 from horizon import exceptions
@@ -399,3 +400,27 @@ class WorkflowsTests(test.TestCase):
 
         flow = WorkflowForTesting(req, entry_point="action_two")
         self.assertEqual("action_two", flow.get_entry_point())
+
+    @override_settings(ALLOWED_HOSTS=['localhost'])
+    def test_redirect_url_safe(self):
+        url = 'http://localhost/test'
+        view = WorkflowViewForTesting()
+        request = self.factory.get("/", data={
+            'next': url,
+        })
+        request.META['SERVER_NAME'] = "localhost"
+        view.request = request
+        context = view.get_context_data()
+        self.assertEqual(url, context['REDIRECT_URL'])
+
+    @override_settings(ALLOWED_HOSTS=['localhost'])
+    def test_redirect_url_unsafe(self):
+        url = 'http://evilcorp/test'
+        view = WorkflowViewForTesting()
+        request = self.factory.get("/", data={
+            'next': url,
+        })
+        request.META['SERVER_NAME'] = "localhost"
+        view.request = request
+        context = view.get_context_data()
+        self.assertIsNone(context['REDIRECT_URL'])

horizon/workflows/views.py

@@ -18,6 +18,7 @@ import json
 from django import forms
 from django import http
 from django import shortcuts
+from django.utils import http as utils_http
 from django.views import generic
 
 from horizon import exceptions
@@ -90,8 +91,15 @@ class WorkflowView(hz_views.ModalBackdropMixin, generic.TemplateView):
         workflow = self.get_workflow()
         workflow.verify_integrity()
         context[self.context_object_name] = workflow
-        next = self.request.GET.get(workflow.redirect_param_name)
+
-        context['REDIRECT_URL'] = next
+        redirect_to = self.request.GET.get(workflow.redirect_param_name)
+        # Make sure the requested redirect is safe
+        if redirect_to and not utils_http.is_safe_url(
+                url=redirect_to,
+                allowed_hosts=[self.request.get_host()]):
+            redirect_to = None
+        context['REDIRECT_URL'] = redirect_to
+
         context['layout'] = self.get_layout()
         # For consistency with Workflow class
         context['modal'] = 'modal' in context['layout']

releasenotes/notes/bug-cd9099c1ba78d637.yaml

@@ -0,0 +1,7 @@
+---
+security:
+  - |
+    An open redirect has been fixed, that could redirect users to arbitrary
+    addresses from certain views by specifying a "next" parameter in the URL.
+    Now the redirect will only work if the target URL is in the same domain,
+    and uses the same protocol.