Zincati is an auto-update agent for Fedora CoreOS hosts. Zincati ships a polkit rule which allows the zincati system user to use the actions org.projectatomic.rpmostree1.deploy to deploy updates to the system and org.projectatomic.rpmostree1.finalize-deployment to reboot the system into the deployed update. Since Zincati v0.0.24, this polkit rule contains a logic error which broadens access of those polkit actions to any unprivileged user rather than just the zincati system user.

In practice, this means that any unprivileged user with access to the system D-Bus socket is able to deploy older Fedora CoreOS versions (which may have other known vulnerabilities). Note that rpm-ostree enforces that the selected version must be from the same branch the system is currently on so this cannot directly be used to deploy an attacker-controlled update payload. This primarily impacts users running untrusted workloads with access to the system D-Bus socket.

Note that in general, untrusted workloads should not be given this access, whether containerized or not. By default, containers do not have access to the system D-Bus socket. The logic error is fixed in Zincati v0.0.30.

A workaround is to manually add a following polkit rule, instructions for which are available in the GitHub Security Advisory.