Apache CloudStack: an account user registering a KVM template executes arbitrary code on the KVM hosts

Impact

By default an ordinary account user may register a template that CloudStack downloads straight to primary storage for instance deployment. The file name is not sanitised, so a crafted template registration runs attacker code on the KVM hosts themselves rather than inside a guest. That is a tenant-to-host escape in a multi-tenant cloud: the attacker lands on the hypervisor that other tenants' instances run on, with reach into primary storage and whatever the host agent can touch. For an accelerator fleet it means a self-service user with nothing but a normal account can take the node that hosts their neighbours' GPU instances, and recovering it means treating the host as compromised, not just rebooting it.

Who can reach it

Any authenticated CloudStack account user who is permitted to register templates - the default configuration - against a zone backed by KVM hosts. No administrative role is needed.

What to do

Upgrade Apache CloudStack to 4.20.3.0 or 4.22.0.1 or later: management-server upgrade plus the host agents, so the control plane restarts and the KVM agents are updated across the fleet. As an interim measure, revoke the ability of non-admin accounts to register templates for direct download to primary storage.

References

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