The Apache CloudStack Proxmox extension improperly trusts a user-editable instance setting, proxmox_vmid, to link CloudStack instances with Proxmox VMs. Because this setting is neither restricted nor validated against tenant ownership and Proxmox VM IDs are predictable, a non-privileged attacker can modify this value to gain unauthorized access to VMs belonging to other tenants. This vulnerability affects Apache CloudStack versions 4.21.0.0 through 4.22.0.0. The attacker can exercise full control over the targeted VM, including starting, stopping, and destroying it. The issue is resolved in Apache CloudStack version 4.22.0.1. A temporary mitigation involves restricting user edits of the proxmox_vmid instance detail via global configuration.

Unauthorized actors can gain cross-tenant access to virtual machines in affected Apache CloudStack deployments using the Proxmox extension. This exposure allows attackers to fully control other tenants' VMs, including operations such as starting, stopping, and destroying these VMs. Such unauthorized control can lead to data exposure, service disruption, and potential loss of tenant resources.

Users should upgrade Apache CloudStack to version 4.22.0.1, which contains the official fix for this vulnerability. For existing installations where immediate upgrade is not possible, administrators can mitigate the risk by preventing users from editing the proxmox_vmid instance detail. This can be done by adding 'proxmox_vmid' to the global configuration parameter 'user.vm.denied.details'. No other actions are specified by the vendor advisory.