T1205.001sub-technique of T1205 Traffic Signaling
Port Knocking
Linux · macOS · Network Devices · Windowsnothing on this site yetT1205.001 on attack.mitre.org
Adversaries may use port knocking to hide open ports used for persistence or command and control. To enable a port, an adversary sends a series of attempted connections to a predefined sequence of closed ports. After the sequence is completed, opening a port is often accomplished by the host based firewall, but could also be implemented by custom software.
If this is happening now
Checklists and playbooks to open while the alert is still live.
Playbook for this stage
Suspicious execution on an endpoint
An EDR alert, an unexplained process, or a user reporting something odd.
how MITRE says to see it
Port-knock → rule/daemon change → first successful connect (T1205.001)
- A remote source rapidly touches a short sequence of closed ports (SYN→RST/S0) on a Windows host. Within a short window the host changes firewall state (WFP rule added/modified or service starts listening) and then the same source completes the first successful handshake to the newly opened port.
- A source performs a short closed-port sequence; the host then modifies iptables/nftables/ufw rules or starts a daemon binding a new socket, followed by a successful connection from the same source.
- A source performs a closed-port sequence; the endpoint enables a PF/socketfilterfw rule or a background process binds a port; then a successful connection completes from the same source.
- Router/switch receives a knock pattern (same src touches device unicast, broadcast, and network-address on same or stepped ports) followed by ACL/line-vty/service enable and the first mgmt session success.
what reduces it
- M1037 Filter Network Traffic. Mitigation of some variants of this technique could be achieved through the use of stateful firewalls, depending upon how it is implemented.