Attack Chain

1. An authenticated attacker with page or media editing permissions initiates a request to the Grav CMS admin interface.
2. The attacker triggers a Flex media handling operation, such as editing a page, that allows media deletion.
3. The attacker intercepts or crafts a POST request to the /admin/pages/[page]/task:save endpoint.
4. The request payload is modified to include a media deletion marker with a key containing path traversal sequences (e.g., ../../data/target.txt).
5. The application’s FlexMediaTrait::saveUpdatedMedia() method processes the deletion queue, passing the unsanitized traversal string to deleteFile().
6. The deleteFile() method validates only the basename (e.g., target.txt), which passes the Utils::checkFilename() filter despite the malicious directory prefix.
7. The doRemove() method concatenates the path and invokes the PHP unlink() function on the resolved path.
8. The underlying filesystem executes the deletion of the target file, outside the authorized media directory.

Impact

Successful exploitation allows an authenticated user to delete critical application files, including configuration files such as user/config/system.yaml or user/config/security.yaml, and user account files. This leads to immediate denial of service or potential privilege escalation by removing security restrictions. The impact is significant for environments where untrusted users are granted administrative-level media management access.

Recommendation

1. Update Grav CMS to the version containing the patch for CVE-2026-72695 immediately.
2. Implement a custom validation logic for the MediaUploadTrait that applies Utils::checkFilename() to the entire file path, as documented in the provided fix.
3. Audit administrative permissions and restrict media management access to strictly vetted users.
4. Monitor web server logs for HTTP POST requests to /admin/pages/ containing path traversal characters like ../ or ..%2f within the payload.