The ocaml binding for the xc_vcpu_getaffinity function in Xen 4.2.x and 4.3.x frees certain memory that may still be intended for use, which allows local users to cause a denial of service (heap corruption and crash) and possibly execute arbitrary code via unspecified vectors that trigger a (1) use-after-free or (2) double free.
http://www.openwall.com/lists/oss-security/2013/10/10/13