Wagtail vulnerable to stored Cross-site Scripting attack via ModelAdmin views

Impact

A stored cross-site scripting (XSS) vulnerability exists on ModelAdmin views within the Wagtail admin interface. A user with a limited-permission editor account for the Wagtail admin could potentially craft pages and documents that, when viewed by a user with higher privileges, could perform actions with that user's credentials. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin, and only affects sites with ModelAdmin enabled.

• For page, the vulnerability is in the "Choose a parent page" ModelAdmin view (ChooseParentView), available when managing pages via ModelAdmin.
• For documents, the vulnerability is in the ModelAdmin Inspect view (InspectView) when displaying document fields.

Patches

Patched versions have been released as Wagtail 4.1.4 (for the LTS 4.1 branch) and Wagtail 4.2.2 (for the current 4.2 branch).

Workarounds

Site owners who are unable to upgrade to the new versions can disable or override the corresponding functionality.

ChooseParentView

For ChooseParentView:

• Disable ModelAdmin for all page models.
• Or provide a custom view via choose_parent_view_class, with the custom view overriding the get_form method.

One of those steps need to be applied for every ModelAdmin class hooked into Wagtail where the model is a Wagtail Page or sub-class. Here is an example of implementing the custom ChooseParentView with patched HTML escaping:

from django import forms
from django.utils.translation import gettext as _
from wagtail.contrib.modeladmin.views import ChooseParentView
from wagtail.contrib.modeladmin.forms import ParentChooserForm


class PatchedPageChoiceField(forms.ModelChoiceField):
    """PageChoiceField with plain-text breadcrumbs to patch stored XSS."""
    def label_from_instance(self, obj):
        bits = []
        for ancestor in (
            obj.get_ancestors(inclusive=True).exclude(depth=1).specific(defer=True)
        ):
            bits.append(ancestor.get_admin_display_title())
        return ' | '.join(bits)


class PatchedParentChooserForm(ParentChooserForm):
    """ParentChooserForm with custom parent_page to patch stored XSS."""
    parent_page = PatchedPageChoiceField(
        label=_("Parent page"),
        required=True,
        empty_label=None,
        queryset=Page.objects.none(),
        widget=forms.RadioSelect(),
    )


class PatchedChooseParentView(ChooseParentView):
    """ChooseParentView with custom get_form patch stored XSS."""
    def get_form(self, request):
        parents = self.permission_helper.get_valid_parent_pages(request.user)
        return PatchedParentChooserForm(parents, request.POST or None)

InspectView

For InspectView:

• Remove inspect_view_enabled=True or set it to False to disable the view.
• Or use inspect_view_fields or inspect_view_fields_exclude to prevent displaying document fields in the views.
• Or provide a custom view via inspect_view_class, with the custom view overriding the get_document_field_display method.

One of those steps need to be applied for every ModelAdmin class hooked into Wagtail where inspect_view_enabled=True. Here is an example of implementing the custom InspectView with patched HTML escaping:

from django.template.defaultfilters import filesizeformat
from django.utils.html import format_html
from wagtail.contrib.modeladmin.views import InspectView


class PatchedInspectView(InspectView):
    """InspectView with override to patch stored XSS vulnerability."""
    def get_document_field_display(self, field_name, field):
        """Render a link to a document"""
        document = getattr(self.instance, field_name)
        if document:
            return format_html(
                '<a href="{}">{} <span class="meta">({}, {})</span></a>',
                document.url,
                document.title,
                document.file_extension.upper(),
                filesizeformat(document.file.size),
            )
        return self.model_admin.get_empty_value_display(field_name)