net/netfilter/nfnetlink_cthelper.c in the Linux kernel through 4.14.4 does not require the CAP_NET_ADMIN capability for new, get, and del operations, which allows local users to bypass intended access restrictions because the nfnl_cthelper_list data structure is shared across all net namespaces.
www.securityfocus.com/bid/102117
access.redhat.com/errata/RHSA-2018:0654
access.redhat.com/errata/RHSA-2018:0676
access.redhat.com/errata/RHSA-2018:1062
patchwork.kernel.org/patch/10089373/
usn.ubuntu.com/3617-1/
usn.ubuntu.com/3617-2/
usn.ubuntu.com/3617-3/
usn.ubuntu.com/3619-1/
usn.ubuntu.com/3619-2/
usn.ubuntu.com/3620-1/
usn.ubuntu.com/3620-2/
usn.ubuntu.com/3632-1/
www.debian.org/security/2017/dsa-4073
www.debian.org/security/2018/dsa-4082