Commonly Used Port
Adversaries may communicate over a commonly used port to bypass firewalls or network detection systems and to blend with normal network activity to avoid more detailed inspection.
They may use commonly open ports such as
- TCP:80 (HTTP)
- TCP:443 (HTTPS)
- TCP:25 (SMTP)
- TCP/UDP:53 (DNS)
They may use the protocol associated with the port or a completely different protocol.
This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.