El pasado 13 de mayo se publicó una vulnerabilidad grave en la FDC, virtual Floppy Disk Controller de QEMU, que podría permitir a un guest ejecutar código arbitrario e inutilizar el host físico en el que se está ejecutando. Red Hat ha publicado un artículo detallando el problema, el impacto en los sistemas y como parchear. Este es un extracto:
A privileged guest user could use this flaw to crash the guest or, potentially, execute arbitrary code on the host with the privileges of the host’s QEMU process corresponding to the guest. It needs to be noted that even if a guest does not explicitly have a virtual floppy disk configured and attached, this issue is exploitable. The problem exists in the Floppy Disk Controller, which is initialized for every x86 and x86_64 guest regardless of the configuration and cannot be removed or disabled.
There is currently no known exploit that would make use of this vulnerability. The sVirt and seccomp functionalities used to restrict host’s QEMU process privileges and resource access might mitigate the impact of successful exploitation of this issue. A possible policy-based workaround is to avoid granting untrusted users administrator privileges within guests.
Procedimiento para parchear los distintos sistemas operativos afectados
CentOS/RHEL/Fedora/Scientific Linux
# yum update
Si sólo queremos actualizar QEMU:
# yum update qemu-kvm
Debian y Ubuntu
# apt-get update && apt-get upgrade
Reinicio de servidor no necesario, VMs, sí
En cualquier caso no es necesario reiniciar el servidor pero sí todas las máquinas virtuales que están en ejecución en el host.