GHSA-f2p5-j6fg-5cxf Wagtail: Denial of service via unbounded filter specs in the image preview

• PyPI wagtail: < 7.0.8 → fixed in 7.0.8 • PyPI wagtail: >= 7.1, < 7.3.3 → fixed in 7.3.3 • PyPI wagtail: >= 7.4, < 7.4.2 → fixed in 7.4.2

Impact An authenticated admin user can trigger expensive rendition processing with purposefully crafted filter specs resulting in potentially service degradation. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin. Patches Patched versions have been released as Wagtail 7.0.8, 7.3.3, 7.4.2. Workarounds For sites that cannot easily upgrade to a current supported version, the vulnerability can be patched by adding the following code to `urls.py` URL pattern declarations to override the vulnerable view. ```python from django.core.exceptions import PermissionDenied from django.http import HttpResponseBadRequest from django.shortcuts import get_object_or_404 from django.urls import path from wagtail.admin import urls as wagtailadmin_urls from wagtail.images.exceptions import InvalidFilterSpecError from wagtail.images.permissions import permission_policy from wagtail.images.views import preview def patched_preview(request, image_id, filter_spec): image = get_object_or_404(get_image_model(), id=image_id) if not permission_policy.user_has_permission_for_instance(request.user, "change", image): raise PermissionDenied try: filter_obj = Filter(spec=filter_spec) except InvalidFilterSpecError: return HttpResponseBadRequest("Invalid filter spec", content_type="text/plain") allowed = {"original", "width", "height", "min", "max", "fill"} if any(operation.method not in allowed for operation in filter_obj.operations): return HttpResponseBadRequest("Invalid filter spec", content_type="text/plain") return preview(request, image_id, filter_spec) urlpatterns = [ # Example where the CMS admin is at /admin/. # Add this before the Wagtail admin URLs registration, with the same sub-path. path("admin/images//preview//", patched_preview) path("admin/", include(wagtailadmin_urls)), ] ``` Acknowledgements Many thanks to @0x1saac for reporting this issue. For more information If you have any questions or comments about this advisory: • Visit Wagtail's support channels • Email us at [email protected] (view our security policy for more information).