The handle_mmio function in arch/x86/hvm/io.c in the MMIO operations emulator for Xen 3.3 and 4.x, when running an HVM guest, does not properly reset certain state information between emulation cycles, which allows local guest OS users to cause a denial of service (guest OS crash) via unspecified operations on MMIO regions.
lists.opensuse.org/opensuse-security-announce/2012-08/msg00024.html
lists.opensuse.org/opensuse-security-announce/2012-08/msg00025.html
lists.opensuse.org/opensuse-security-announce/2012-09/msg00017.html
lists.opensuse.org/opensuse-security-announce/2012-09/msg00018.html
lists.xen.org/archives/html/xen-devel/2012-07/msg01649.html
secunia.com/advisories/55082
security.gentoo.org/glsa/glsa-201309-24.xml
www.debian.org/security/2012/dsa-2531
www.securityfocus.com/bid/54691