Executive brief
Craft CMS is a content management system used to build websites and manage digital content. A flaw in its access control system allows users with read-only permission on another author's content to reorder Matrix or Address nested elements within that content—a write operation they should not be able to perform. An attacker needs to view the content once, which automatically grants the system permission to reorder nested elements, enabling unauthorized data modification.
Technical details
A missing authorization check in Craft CMS's actions/nested-elements/reorder endpoint allows authenticated users with limited permissions to modify nested content they should not be able to edit. When a user with viewPeerEntries (view other authors' entries) but without savePeerEntries (edit other authors' entries) opens another author's entry in read-only mode, Craft grants a manageNestedElements session flag for Matrix/Address fields. The reorder endpoint trusts this flag alone without rechecking the caller's actual save permission, unlike the delete endpoint which performs proper authorization. An attacker can then POST to the reorder endpoint using parameters visible in the read-only page source to change the sort order of nested elements. Craft CMS 5.10.13 and later include the fix.
Affected products
- Craft CMS 5.0.0 through 5.10.12
Timeline
- 2026-09-16: disclosed
- 2026-09-16: patched: Fixed in version 5.10.13