WinPVDrivers: Excessive permissions on user-exposed devices

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] The Windows PV drivers expose various facilities to userspace. Several of these have no security descriptor, and are therefore fully accessible to unprivileged users. These are: 1. XenCons, CVE-2025-27462 2. XenIface, CVE-2025-27463 3. XenBus, CVE-2025-27464