cloud-init through 25.1.2 includes the systemd socket unit cloud-init-hotplugd.socket with default SocketMode that grants 0666 permissions, making it world-writable. This is used for the "/run/cloud-init/hook-hotplug-cmd" FIFO. An unprivileged user could trigger hotplug-hook commands.
The product specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.