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Commonly Used Port
|Commonly Used Port|
|Tactic||Command and Control|
|Data Sources||Network Traffic: Network Traffic Flow|
|External Contributors||Matan Dobrushin - Otorio|
|Asset||Safety Instrumented System/Protection Relay, Field Controller/RTU/PLC/IED, Human-Machine Interface, Control Server, Engineering Workstation|
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.
- TCP:80 (HTTP)
- TCP:443 (HTTPS)
- TCP/UDP:53 (DNS)
- TCP:1024-4999 (OPC on XP/Win2k3)
- TCP:49152-65535 (OPC on Vista and later)
- TCP:23 (TELNET)
- UDP:161 (SNMP)
- TCP:502 (MODBUS)
- TCP:102 (S7comm/ISO-TSAP)
- TCP:20000 (DNP3)
- TCP:44818 (Ethernet/IP)
- Dragonfly 2.0 communicated with command and control over TCP ports 445 and 139 or UDP 137 or 138.1
- Stuxnet attempts to contact command and control servers on port 80 to send basic information about the computer it has compromised.2
- Triton uses TriStation’s default UDP port, 1502, to communicate with devices.3
- 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.
- Disable or Remove Feature or Program - Ensure that unnecessary ports and services are closed to prevent risk of discovery and potential exploitation.
- 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.4
- 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.
- Cybersecurity & Infrastructure Security Agency. (2018, March 15). Alert (TA18-074A) Russian Government Cyber Activity Targeting Energy and Other Critical Infrastructure Sectors. Retrieved October 11, 2019.
- Nicolas Falliere, Liam O Murchu, Eric Chien. (2011, February). W32.Stuxnet Dossier (Version 1.4). Retrieved September 22, 2017.