A flaw was found in the libvirt nwfilter driver

A flaw was found in the libvirt nwfilter driver. The virNWFilterObjListNumOfNWFilters method failed to acquire the driver->nwfilters mutex before iterating over virNWFilterObj instances. There was no protection to stop another thread from concurrently modifying the driver->nwfilters object. This flaw allows a malicious, unprivileged user to exploit this issue via libvirt's API virConnectNumOfNWFilters to crash the network filter management daemon (libvirtd/virtnwfilterd).