Red Hat libvirt, possibly 0.6.0 through 0.8.2, creates new images without setting the user-defined backing-store format, which allows guest OS users to read arbitrary files on the host OS via unspecified vectors.
libvirt.org/news.html
lists.fedoraproject.org/pipermail/package-announce/2010-July/044520.html
lists.fedoraproject.org/pipermail/package-announce/2010-July/044579.html
lists.opensuse.org/opensuse-security-announce/2010-09/msg00006.html
ubuntu.com/usn/usn-1008-1
ubuntu.com/usn/usn-1008-2
ubuntu.com/usn/usn-1008-3
www.redhat.com/support/errata/RHSA-2010-0615.html
www.vupen.com/english/advisories/2010/2062
www.vupen.com/english/advisories/2010/2763
bugzilla.redhat.com/show_bug.cgi?id=607812