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. Updating a Docker-based Ghost instance is documented here.

If your Ghost is a Ghost-CLI install see our documentation on updating it to the latest version here.

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.