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).