Adversaries may communicate over a commonly used port to bypass firewalls or network detection systems and to blend in with normal network activity, to avoid more detailed inspection. They may use the protocol associated with the port, or a completely different protocol. They may use commonly open ports, such as the examples provided below.
| ID | Name | Description |
|---|---|---|
| C0028 | 2015 Ukraine Electric Power Attack |
During the 2015 Ukraine Electric Power Attack, Sandworm Team used port 443 to communicate with their C2 servers. [1] |
| C0063 | 2025 Poland Wiper Attacks |
During the 2025 Poland Wiper Attacks, the adversaries enabled TCP port 445 on Mikronika HMI devices creating a new firewall rule named "Microsoft Update".[2] |
| G1027 | CyberAv3ngers |
During the 2026 Iranian Water Campaign, CyberAv3ngers were observed using secure shell ports TCP/22 and common industrial ports (TCP/44818, TCP&UDP/2222, TCP/102, and TCP/502). [3] |
| S1165 | FrostyGoop |
FrostyGoop communicates using the Modbus protocol over the standard port of TCP 502.[4] |
| S0603 | Stuxnet |
Stuxnet attempts to contact command and control servers on port 80 to send basic information about the computer it has compromised. [5] |
| S1009 | Triton |
Triton uses TriStations default UDP port, 1502, to communicate with devices.[6] |
| ID | Mitigation | Description |
|---|---|---|
| M0942 | Disable or Remove Feature or Program |
Ensure that unnecessary ports and services are closed to prevent risk of discovery and potential exploitation. |
| M0804 | Human User Authentication |
All field controllers should require users to authenticate for all remote or local management sessions. The authentication mechanisms should also support Account Use Policies, Password Policies, and User Account Management. |
| M0931 | Network Intrusion Prevention |
Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level. Signatures are often for unique indicators within protocols and may be based on the specific protocol used by a particular adversary or tool and will likely be different across various malware families and versions. Adversaries will likely change tool C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools.[7] |
| M0930 | Network Segmentation |
Configure internal and external firewalls to block traffic using common ports that associate to network protocols that may be unnecessary for that particular network segment. |
| ID | Name | Analytic ID | Analytic Description |
|---|---|---|---|
| DET0736 | Detection of Commonly Used Port | AN1869 |
Real-time monitoring identifies an Industrial Control System (ICS) host or server establishing outbound connections on a commonly-allowed port (e.g., 443, 80, 8080, 53, etc.) to a destination not in the approved vendor/business domain list, where that host's documented network role does not require external connectivity. Documented real-world use: Sandworm's 2015 Ukraine power grid attack used port 443 for Command and Control (C2) communications. OT operational-fidelity gate: Alert only when the asset's documented role does not permit the connection and the destination/proxy/service is outside the approved communications profile, with process/service identity used as corroboration where available. Suppress approved vendor support, update repositories, remote operations, failover paths, and documented temporary connectivity. SNI and certificate attributes are TLS/session metadata; do not treat them as decrypted payload content. Encrypted application content requires a separate inspection point. |
| AN2129 |
Real-time monitoring identifies an Industrial Control System (ICS) Linux service process initiating an outbound connection on a commonly-used port to a destination not in the approved vendor domain list. OT operational-fidelity gate: Alert only when the asset's documented role does not permit the connection and the destination/proxy/service is outside the approved communications profile, with process/service identity used as corroboration where available. Suppress approved vendor support, update repositories, remote operations, failover paths, and documented temporary connectivity. |
||
| AN2221 |
Real-time monitoring identifies an embedded field device initiating outbound connections on a commonly-used port to a destination outside the device's documented operational communication profile, which for most embedded Industrial Control System (ICS) devices normally should not include arbitrary outbound internet connectivity under the approved communications architecture. OT operational-fidelity gate: Alert only when the asset's documented role does not permit the connection and the destination/proxy/service is outside the approved communications profile, with process/service identity used as corroboration where available. Suppress approved vendor support, update repositories, remote operations, failover paths, and documented temporary connectivity. |
||
| AN2271 |
Real-time monitoring identifies an Industrial Control System (ICS) vendor process making outbound connections on commonly-allowed port (e.g., 80, 443, 8080, etc.) to a destination not in the approved vendor domain list, from a host whose documented role does not require external connectivity. OT operational-fidelity gate: Alert only when the asset's documented role does not permit the connection and the destination/proxy/service is outside the approved communications profile, with process/service identity used as corroboration where available. Suppress approved vendor support, update repositories, remote operations, failover paths, and documented temporary connectivity. |