The libxl toolstack library in Xen 4.1.x through 4.6.x does not properly release mappings of files used as kernels and initial ramdisks when managing multiple domains in the same process, which allows attackers to cause a denial of service (memory and disk consumption) by starting domains.
Debian Linux Security Advisory 3519-1 - Multiple security issues have been found in the Xen virtualisation solution, which may result in denial of service or information disclosure.