An out-of-bounds access issue was found in the Linux kernel, all versions
through 5.3, in the way Linux kernel's KVM hypervisor implements the
Coalesced MMIO write operation. It operates on an MMIO ring buffer 'struct
kvm_coalesced_mmio' object, wherein write indices 'ring->first' and
'ring->last' value could be supplied by a host user-space process. An
unprivileged host user or process with access to '/dev/kvm' device could
use this flaw to crash the host kernel, resulting in a denial of service or
potentially escalating privileges on the system.

Matt Delco discovered that the KVM hypervisor implementation in the Linux
kernel did not properly perform bounds checking when handling coalesced
MMIO write operations. A local attacker with write access to /dev/kvm could
use this to cause a denial of service (system crash).

Ensure that untrusted users cannot write to the /dev/kvm device

tyhicks

An attacker needs write access to the /dev/kvm device file to exploit this flaw. By default, Ubuntu users don't have privileges to write to /dev/kvm. This is true even when libvirt is installed and in use.