Why containers are less secure that virtual machine?

Containers do not expose a larger host OS attack surface than VMs - they actually reduce OS-layer exposure by eliminating guest OS stacks, though they do share the host kernel.

Attachment to a shared virtual network is a configurable property common to both containers and VMs and is not an inherent security disadvantage unique to containers.

Disk space exhaustion is a resource management concern that can be mitigated with storage quotas on both containers and VMs and does not represent a security weakness specific to containers.

Because containers share the host OS kernel and lack the strict resource isolation enforced by a hypervisor, a compromised or malicious container can consume excessive CPU cycles and starve the host and co-located containers of processing resources. This type of denial-of-service impact on the host is not possible with fully isolated VMs because the hypervisor enforces hard resource boundaries between guest and host.