CVE-2020-15118: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (CWE-79)
value: In Wagtail before versions 2.7.4 and 2.9.3, when a form page type is made available to Wagtail editors through the `wagtail.contrib.forms` app, and the page template is built using Django's standard form rendering helpers such as form.as_p, any HTML tags used within a form field's help text will be rendered unescaped in the page. Allowing HTML within help text is an intentional design decision by Django; however, as a matter of policy Wagtail does not allow editors to insert arbitrary HTML by default, as this could potentially be used to carry out cross-site scripting attacks, including privilege escalation. This functionality should therefore not have been made available to editor-level users. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin. Patched versions have been released as Wagtail 2.7.4 (for the LTS 2.7 branch) and Wagtail 2.9.3 (for the current 2.9 branch). In these versions, help text will be escaped to prevent the inclusion of HTML tags. Site owners who wish to re-enable the use of HTML within help text (and are willing to accept the risk of this being exploited by editors) may set WAGTAILFORMS_HELP_TEXT_ALLOW_HTML = True in their configuration settings. Site owners who are unable to upgrade to the new versions can secure their form page templates by rendering forms field-by-field as per Django's documentation, but omitting the |safe filter when outputting the help text.
CWE description: The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
CVSS v3 base score: 5.4
Published: 2020-07-20T18:15Z
Repository: https://github.com/wagtail/wagtail
Language: Python
Files changed: docs/reference/settings.rst, wagtail/contrib/forms/forms.py, wagtail/contrib/forms/tests/test_models.py, wagtail/contrib/forms/tests/utils.py
Commit date: 2020-07-20 10:36:28 +0100
Commit message: Escape help text in form builder forms by default

This can be disabled with the setting WAGTAILFORMS_HELP_TEXT_ALLOW_HTML

Diff: diff --git a/docs/reference/settings.rst b/docs/reference/settings.rst
index 00b27683f..cfdaa71e9 100644
--- a/docs/reference/settings.rst
+++ b/docs/reference/settings.rst
@@ -545,5 +545,18 @@ Redirects
 By default the redirect importer keeps track of the uploaded file as a temp file, but on certain environments (load balanced/cloud environments), you cannot keep a shared file between environments. For those cases you can use the built-in cache to store the file instead.
 
 .. code-block:: python
 
    WAGTAIL_REDIRECTS_FILE_STORAGE = 'cache'
+
+Form builder
+============
+
+.. versionadded:: 2.7.4/2.9.3
+
+    The ``WAGTAILFORMS_HELP_TEXT_ALLOW_HTML`` option was added.
+
+.. code-block:: python
+
+    WAGTAILFORMS_HELP_TEXT_ALLOW_HTML = True
+
+When true, HTML tags in form field help text will be rendered unescaped (default: False).
diff --git a/wagtail/contrib/forms/forms.py b/wagtail/contrib/forms/forms.py
index cbd980280..3446fe741 100644
--- a/wagtail/contrib/forms/forms.py
+++ b/wagtail/contrib/forms/forms.py
@@ -1,8 +1,10 @@
 from collections import OrderedDict
 
 import django.forms
+from django.conf import settings
+from django.utils.html import conditional_escape
 from django.utils.translation import gettext_lazy as _
 
 from wagtail.admin.forms import WagtailAdminPageForm
 from wagtail.contrib.forms.utils import get_field_clean_name
 
@@ -112,11 +114,14 @@ class FormBuilder:
         return formfields
 
     def get_field_options(self, field):
         options = {}
         options['label'] = field.label
-        options['help_text'] = field.help_text
+        if getattr(settings, 'WAGTAILFORMS_HELP_TEXT_ALLOW_HTML', False):
+            options['help_text'] = field.help_text
+        else:
+            options['help_text'] = conditional_escape(field.help_text)
         options['required'] = field.required
         options['initial'] = field.default_value
         return options
 
     def get_form_class(self):
diff --git a/wagtail/contrib/forms/tests/test_models.py b/wagtail/contrib/forms/tests/test_models.py
index 08523130c..822078b9b 100644
--- a/wagtail/contrib/forms/tests/test_models.py
+++ b/wagtail/contrib/forms/tests/test_models.py
@@ -27,13 +27,22 @@ class TestFormSubmission(TestCase):
         # Check response
         self.assertContains(response, """<label for="id_your_email">Your email</label>""")
         self.assertTemplateUsed(response, 'tests/form_page.html')
         self.assertTemplateNotUsed(response, 'tests/form_page_landing.html')
 
+        # HTML in help text should be escaped
+        self.assertContains(response, "&lt;em&gt;please&lt;/em&gt; be polite")
+
         # check that variables defined in get_context are passed through to the template (#1429)
         self.assertContains(response, "<p>hello world</p>")
 
+    @override_settings(WAGTAILFORMS_HELP_TEXT_ALLOW_HTML=True)
+    def test_get_form_without_help_text_escaping(self):
+        response = self.client.get('/contact-us/')
+        # HTML in help text should not be escaped
+        self.assertContains(response, "<em>please</em> be polite")
+
     def test_post_invalid_form(self):
         response = self.client.post('/contact-us/', {
             'your_email': 'bob',
             'your_message': 'hello world',
             'your_choices': ''
diff --git a/wagtail/contrib/forms/tests/utils.py b/wagtail/contrib/forms/tests/utils.py
index 809ecf0c6..e212ecce5 100644
--- a/wagtail/contrib/forms/tests/utils.py
+++ b/wagtail/contrib/forms/tests/utils.py
@@ -26,10 +26,11 @@ def make_form_page(**kwargs):
         page=form_page,
         sort_order=2,
         label="Your message",
         field_type='multiline',
         required=True,
+        help_text="<em>please</em> be polite"
     )
     FormField.objects.create(
         page=form_page,
         sort_order=3,
         label="Your choices",

Vulnerable code:         options['help_text'] = field.help_text
Fixed code: 
Form builder
============

.. versionadded:: 2.7.4/2.9.3

    The ``WAGTAILFORMS_HELP_TEXT_ALLOW_HTML`` option was added.

.. code-block:: python

    WAGTAILFORMS_HELP_TEXT_ALLOW_HTML = True

When true, HTML tags in form field help text will be rendered unescaped (default: False).
from django.conf import settings
from django.utils.html import conditional_escape
        if getattr(settings, 'WAGTAILFORMS_HELP_TEXT_ALLOW_HTML', False):
            options['help_text'] = field.help_text
        else:
            options['help_text'] = conditional_escape(field.help_text)
        # HTML in help text should be escaped
        self.assertContains(response, "&lt;em&gt;please&lt;/em&gt; be polite")

    @override_settings(WAGTAILFORMS_HELP_TEXT_ALLOW_HTML=True)
    def test_get_form_without_help_text_escaping(self):
        response = self.client.get('/contact-us/')
        # HTML in help text should not be escaped
        self.assertContains(response, "<em>please</em> be polite")

        help_text="<em>please</em> be polite"