CVE-2026-31692 is a vulnerability in the Linux kernel's rtnetlink subsystem where the function rtnl_newlink lacks a capability check (CAP_NET_ADMIN) on the peer network namespace when creating paired network devices such as veth, vxcan, and netkit. This flaw allows an unprivileged user with a user namespace to create network interfaces in arbitrary network namespaces, including the init_net namespace. The issue is addressed by adding a netlink_ns_capable() check for CAP_NET_ADMIN in the peer namespace before permitting device creation.