GHSA-w6fv-6gcc-x825

Impact

Zincati ships a polkit rule which allows the zincati system user to use the following actions: - org.projectatomic.rpmostree1.deploy: used to deploy updates to the system - org.projectatomic.rpmostree1.finalize-deployment: used 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.

Patches

The logic error is fixed in Zincati v0.0.30. The fix is included in the following FCOS releases: - On the stable stream: 41.20250302.3.2 - On the testing stream: 41.20250315.2.0 - On the next stream: 42.20250316.1.0

Workarounds

A workaround is to add the following polkit rule:

polkit.addRule(function(action, subject) {
    if (action.id == "org.projectatomic.rpmostree1.deploy" ||
        action.id == "org.projectatomic.rpmostree1.finalize-deployment" ||
        action.id == "org.projectatomic.rpmostree1.cleanup") {
        if (subject.user != "zincati") {
                return polkit.Result.NO;
        }
    }
});

to e.g. /etc/polkit-1/rules.d/00-zincati-fix.rules (it must sort earlier than zincati.rules lexicographically).

Note that this rule will deny all non-root users other than zincati from using those actions. If you've added polkit rules to allow e.g. the core user or other users, you will need to adjust the policy (or make sure the ordering is appropriate).

References

This issue was introduced by this commit, and is fixed in v0.0.30.