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.
Debian Linux Security Advisory 3006-1 - Multiple security issues have been discovered in the Xen virtualisation solution which may result in information leaks or denial of service.