Ghost Content API filter bypass reveals private fields

### Impact The validation applied to filters on the public API endpoints could be partially bypassed, making it possible to reveal private fields via a brute force attack. If SQLite was used as the database password hashes were fully accessible. If MySQL was used as the database the password hashes' case (uppercase / lowercase) would have been lost, which would likely have rendered a further brute force attack on the discovered hashes fruitless. ### Vulnerable versions This vulnerability is present in Ghost from v5.46.1 up to v6.21.1. ### Patches v6.21.2 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). ### Workarounds If upgrading immediately is not possible, block or filter requests to Content API endpoints where the `filter` query parameter contains `password` or `email` (including any compound form such as `users.password`, `users.email`, `authors.password`, `authors.email`). Reject requests at a reverse proxy / WAF layer before they reach Ghost. Example (case-insensitive) pattern to block on the raw querystring: ``` filter=[^&]*(password|email) ``` ### References Ghost thanks crnkovic for disclosing this vulnerability responsibly. ### For more information If you have any questions or comments about this advisory, email Ghost at [security@ghost.org](mailto:security@ghost.org).