The backend driver in Xen 3.x allows guest OS users to cause a denial of service via a kernel thread leak, which prevents the device and guest OS from being shut down or create a zombie domain, causes a hang in zenwatch, or prevents unspecified xm commands from working properly, related to (1) netback, (2) blkback, or (3) blktap.
lists.opensuse.org/opensuse-security-announce/2011-01/msg00007.html
secunia.com/advisories/42372
secunia.com/advisories/42789
secunia.com/advisories/43056
secunia.com/advisories/46397
www.redhat.com/support/errata/RHSA-2011-0004.html
www.securityfocus.com/archive/1/520102/100/0/threaded
www.securityfocus.com/bid/45039
www.securitytracker.com/id?1024786
www.vmware.com/security/advisories/VMSA-2011-0012.html
www.vupen.com/english/advisories/2011/0024
www.vupen.com/english/advisories/2011/0213
xenbits.xensource.com/linux-2.6.18-xen.hg?rev/59f097ef181b