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.
This technique has been observed to both for the dynamic opening of a listening port as well as the initiating of a connection to a listening server on a different system.
The observation of the signal packets to trigger the communication can be conducted through different methods. One means, originally implemented by Cd00r (Citation: Hartrell cd00r 2002), is to use the libpcap libraries to sniff for the packets in question. Another method leverages raw sockets, which enables the malware to use ports that are already open for use by other programs.
View in MITRE ATT&CK®| Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name | Notes |
|---|---|---|---|---|---|
| AC-3 | Access Enforcement | Protects | T1205.001 | Port Knocking | |
| AC-4 | Information Flow Enforcement | Protects | T1205.001 | Port Knocking | |
| CA-7 | Continuous Monitoring | Protects | T1205.001 | Port Knocking | |
| CM-6 | Configuration Settings | Protects | T1205.001 | Port Knocking | |
| CM-7 | Least Functionality | Protects | T1205.001 | Port Knocking | |
| SC-7 | Boundary Protection | Protects | T1205.001 | Port Knocking | |
| SI-15 | Information Output Filtering | Protects | T1205.001 | Port Knocking | |
| SI-4 | System Monitoring | Protects | T1205.001 | Port Knocking | |
| network_security_groups | Network Security Groups | technique_scores | T1205.001 | Port Knocking |
Comments
This control can be used to implement whitelist based network rules that can mitigate variations of this sub-techniques that result in opening closed ports for communication. Because this control is able to drop traffic before reaching a compromised host, it can effectively mitigate this port knocking sub-technique.
References
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| azure_firewall | Azure Firewall | technique_scores | T1205.001 | Port Knocking |
Comments
This control can protect against this sub-technique by enforcing limited access to only required ports. Consequently, even if the adversary is able to utilize port knocking to open additional ports at the host level, it is still blocked at the firewall service level. This service typically applies to external traffic and not internal traffic and therefore lateral movement using this technique within a network is still possible. Due to this partial coverage, it has been scored as Partial.
References
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