Paolo Bonzini of Red Hat discovered that the blit region checks were
insufficient in the Cirrus VGA emulator in qemu-kvm, a full
virtualization solution on x86 hardware. A privileged guest user could
use this flaw to write into qemu address space on the host, potentially
escalating their privileges to those of the qemu host process.
For the stable distribution (wheezy), this problem has been fixed in
version 1.1.2+dfsg-6+deb7u6.
We recommend that you upgrade your qemu-kvm packages.