The __netlink_deliver_tap_skb function in net/netlink/af_netlink.c in the
Linux kernel through 4.14.4, when CONFIG_NLMON is enabled, does not
restrict observations of Netlink messages to a single net namespace, which
allows local users to obtain sensitive information by leveraging the
CAP_NET_ADMIN capability to sniff an nlmon interface for all Netlink
activity on the system.

It was discovered that the netlink subsystem in the Linux kernel did not
properly restrict observations of netlink messages to the appropriate net
namespace. A local attacker could use this to expose sensitive information
(kernel netlink traffic).