The __ip6_append_data function in net/ipv6/ip6_output.c in the Linux kernel
through 4.11.3 is too late in checking whether an overwrite of an skb data
structure may occur, which allows local users to cause a denial of service
(system crash) via crafted system calls.

It was discovered that the IPv6 stack in the Linux kernel was performing
its over write consistency check after the data was actually overwritten. A
local attacker could exploit this flaw to cause a denial of service (system
crash).