Craft CMS is a content management system (CMS). From 5.0.0-RC1 to before 5.9.18, AssetsController::actionShowInFolder() fetches an asset by ID and returns its filename and complete folder hierarchy (including volume handle, volume UID, folder names, folder UIDs, and folder URI paths) without checking whether the requesting user has viewAssets or viewPeerAssets permission on the asset’s volume. Any authenticated CP user — even one with zero volume permissions — can enumerate asset filenames and the full folder structure of any volume by supplying arbitrary asset IDs. This vulnerability is fixed in 5.9.18.