Flatpak writes the OCI repository authentication token with world-readable permissions (0644) in the system-helper's cache directory, allowing other local users on a multi-user system to read the token and impersonate the authenticated user against the OCI repository. Only OCI-based sources (e.g. as used by Fedora) are affected; libostree-based sources such as Flathub are not.
https://github.com/flatpak/flatpak/security/advisories/GHSA-7rvf-rqr3-43j4