libspice, as used in QEMU-KVM in Red Hat Enterprise Virtualization Hypervisor (aka RHEV-H or rhev-hypervisor) before 5.5-2.2 and possibly other products, allows guest OS users to read from or write to arbitrary QEMU memory by modifying the address that is used by Cairo for memory mappings.
https://rhn.redhat.com/errata/RHSA-2010-0476.html