Update ManagementForm to validate current_step

Previously, bots could and would stuff this form value with all kinds of nonsense, triggering a server error (and subsequent alert emails).
Supersedes jazzband#47

formtools/wizard/forms.py

@@ -1,9 +1,20 @@
 from django import forms
+from django.core.exceptions import ValidationError
 
 
 class ManagementForm(forms.Form):
     """
     ``ManagementForm`` is used to keep track of the current wizard step.
     """
+    def __init__(self, steps, **kwargs):
+        self.steps = steps
+        super().__init__(**kwargs)
+
     template_name = "django/forms/p.html"  # Remove when Django 5.0 is minimal version.
     current_step = forms.CharField(widget=forms.HiddenInput)
+
+    def clean_current_step(self):
+        data = self.cleaned_data['current_step']
+        if data not in self.steps:
+            raise ValidationError("Invalid step name.")
+        return data

formtools/wizard/views.py

@@ -45,12 +45,12 @@ def __repr__(self):
 
     @property
     def all(self):
-        "Returns the names of all steps/forms."
+        """Returns the names of all steps/forms."""
         return list(self._wizard.get_form_list())
 
     @property
     def count(self):
-        "Returns the total number of steps/forms in this the wizard."
+        """Returns the total number of steps/forms in this the wizard."""
         return len(self.all)
 
     @property
@@ -63,27 +63,27 @@ def current(self):
 
     @property
     def first(self):
-        "Returns the name of the first step."
+        """Returns the name of the first step."""
         return self.all[0]
 
     @property
     def last(self):
-        "Returns the name of the last step."
+        """Returns the name of the last step."""
         return self.all[-1]
 
     @property
     def next(self):
-        "Returns the next step."
+        """Returns the next step."""
         return self._wizard.get_next_step()
 
     @property
     def prev(self):
-        "Returns the previous step."
+        """Returns the previous step."""
         return self._wizard.get_prev_step()
 
     @property
     def index(self):
-        "Returns the index for the current step."
+        """Returns the index for the current step."""
         return self._wizard.get_step_index()
 
     @property
@@ -277,7 +277,7 @@ def post(self, *args, **kwargs):
             return self.render_goto_step(wizard_goto_step)
 
         # Check if form was refreshed
-        management_form = ManagementForm(self.request.POST, prefix=self.prefix)
+        management_form = ManagementForm(steps=self.steps.all, data=self.request.POST, prefix=self.prefix)
         if not management_form.is_valid():
             raise SuspiciousOperation(_('ManagementForm data is missing or has been tampered.'))
 
@@ -576,7 +576,7 @@ def get_context_data(self, form, **kwargs):
         context['wizard'] = {
             'form': form,
             'steps': self.steps,
-            'management_form': ManagementForm(prefix=self.prefix, initial={
+            'management_form': ManagementForm(steps=self.steps.all, prefix=self.prefix, initial={
                 'current_step': self.steps.current,
             }),
         }

tests/wizard/wizardtests/tests.py

@@ -73,6 +73,18 @@ def test_form_post_mgmt_data_missing(self):
         # view should return HTTP 400 Bad Request
         self.assertEqual(response.status_code, 400)
 
+    def test_invalid_step_data(self):
+        wizard_step_data = self.wizard_step_data[0].copy()
+
+        # Replace the current step with invalid data
+        for key in list(wizard_step_data.keys()):
+            if "current_step" in key:
+                wizard_step_data[key] = "not-a-valid-step"
+
+        response = self.client.post(self.wizard_url, wizard_step_data)
+        # view should return HTTP 400 Bad Request
+        self.assertEqual(response.status_code, 400)
+
     def test_form_post_success(self):
         response = self.client.post(self.wizard_url, self.wizard_step_data[0])
         wizard = response.context['wizard']