OpenStack Magnum passes OpenStack credentials into the Heat templates creating its instances. While these should just be used for retrieving the instances' SSL certificates, they allow full API access, though and can be used to perform any API operation the user is authorized to perform.
A flaw was found in the way memory was being allocated on the stack for user space binaries. If heap and stack memory regions were adjacent to each other, an attacker could use this flaw to jump over the heap/stack gap, cause controlled memory corruption on process stack or heap, and thus increase their privileges on the system.
This is a tracking bug for the glibc part of the mitigation.