The libxenlight (libxl) toolstack library in Xen 4.0.x, 4.1.x, and 4.2.x uses weak permissions for xenstore keys for paravirtualised and emulated serial console devices, which allows local guest administrators to modify the xenstore value via unspecified vectors.
http://www.openwall.com/lists/oss-security/2013/06/26/4
http://www.openwall.com/lists/oss-security/2013/06/25/1
http://www.debian.org/security/2014/dsa-3006
http://security.gentoo.org/glsa/glsa-201309-24.xml
http://secunia.com/advisories/55082
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00021.html