A flaw was found in the way NTP handled rate limiting. An attacker able to send a large number of crafted requests to an NTP server could trigger the rate limiting on that server, and prevent clients from getting a usable reply from the server.

The default NTP configuration in Red Hat Enterprise Linux does not enable rate limiting.

External References:

https://www.cs.bu.edu/~goldbe/NTPattack.html

The ntpd client in NTP 4.x before 4.2.8p4 and 4.3.x before 4.3.77 allows remote attackers to cause a denial of service via a number of crafted "KOD" messages.

The paginginvlpg function in include/asm-x86/paging.h in Xen 3.3.x through 4.6.x, when using shadow mode paging or nested virtualization is enabled, allows local HVM guest users to cause a denial of service (host crash) via a non-canonical guest address in an INVVPID instruction, which triggers a hypervisor bug check.

QEMU does not properly restrict write access to the PCI config space for certain PCI pass-through devices, which might allow local x86 HVM guests to gain privileges, cause a denial of service (host crash), obtain sensitive information, or possibly have other unspecified impact via unknown vectors.