kernel: Missing capabilities check in net/netfilter/nfnetlink_cthelper.c allows for unprivileged access to systemwide nfnl_cthelper_list structure

The net/netfilter/nfnetlinkcthelper.c function in the Linux kernel through 4.14.4 does not require the CAPNETADMIN capability for new, get, and del operations. This allows local users to bypass intended access restrictions because the nfnlcthelperlist data structure is shared across all net...