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.

An attacker can exploit this by crafting malicious Markdown image syntax that includes path traversal sequences. This allows the application to resolve and process files located outside of the designated media directory. The system subsequently composites the unauthorized file into a carrier image, caches the resulting file, and serves it through a public-facing, unauthenticated URL. This leads to the unauthorized disclosure of sensitive image data residing on the web server to remote anonymous visitors.

Attack Chain

1. Attacker identifies a Grav CMS instance running version 2.0.10.
2. Attacker authors a malicious Markdown document containing a crafted image tag.
3. The image tag includes directory traversal sequences (e.g., ../../) in the watermark parameter.
4. The ImageMedium::watermark() method receives the malicious payload.
5. The input is passed to UniformResourceLocator::findResource(), which fails to validate the traversal path.
6. The application resolves the path to an image file outside the intended web root or media sandbox.
7. The server processes and composites the unauthorized image into a new file.
8. The final file is cached and exposed via a public URL, allowing the attacker to download the sensitive content.

Impact

Successful exploitation allows for the unauthenticated disclosure of any image file accessible to the web server process. This could result in the exposure of private administrative images, sensitive site metadata, or other assets not intended for public consumption. Given the CVSS score of 7.5, this poses a high risk to data confidentiality for affected web platforms.

Recommendation

Prioritize the identification of all internet-facing instances of Grav CMS version 2.0.10 and upgrade to the latest patched version immediately. Monitor web server access logs for anomalous requests containing path traversal sequences (e.g., ../) targeting image processing parameters or Markdown-related endpoints. Ensure that web server file system permissions follow the principle of least privilege to restrict the web user's access to files outside of the defined document root.