CVE-2017-12188 (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2017-12188): arch/x86/kvm/mmu.c in the Linux kernel through 4.13.5, when nested virtualisation is used, does not properly traverse guest pagetable entries to resolve a guest virtual address, which allows L1 guest OS users to execute arbitrary code on the host OS or cause a denial of service (incorrect index during page walking, and host OS crash), aka an "MMU potential stack buffer overrun."
Fixed in 4.9.57, 4.14