A denial of service vulnerability was discovered in nbdkit 1.12.7, 1.14.1 and 1.15.1. An attacker could connect to the nbdkit service and cause it to perform a large amount of work in initializing backend plugins, by simply opening a connection to the service. This vulnerability could cause resource consumption and degradation of service in nbdkit, depending on the plugins configured on the server-side.
https://www.redhat.com/archives/libguestfs/2019-September/msg00084.html