The /charms endpoint on a Juju controller lacked sufficient authorization checks, allowing any user with an account on the controller to upload a charm. Uploading a malicious charm that exploits a Zip Slip vulnerability could allow an attacker to gain access to a machine running a unit through the affected charm.
https://github.com/juju/juju/security/advisories/GHSA-24ch-w38v-xmh8