GHSA-944x-pm95-3jpr

### Impact

Insufficient validation of the client-supplied `Content-Type` on Ghost's Admin API file upload endpoint allowed uploaded files to be served from the site with an attacker-chosen content type on S3/GCS storage backends. On installations that serve uploaded files from the same origin as the site, this could have been used to facilitate stored cross-site scripting against site visitors or staff.

### Vulnerable versions

This vulnerability is present in Ghost from v6.19.4 up to v6.21.0.

### Patches

v6.21.1 contains a fix for this issue.

### How to update

For self-hosters using Docker, find [Docker's official Ghost image here](https://hub.docker.com/_/ghost). Updating a Docker-based Ghost instance [is documented here](https://docs.ghost.org/install/docker#updating-ghost).

If your Ghost is a Ghost-CLI install see our documentation on [updating it to the latest version here](https://docs.ghost.org/update).

### For more information

If you have any questions or comments about this advisory, email us at [security@ghost.org](mailto:security@ghost.org).