Adversaries may perform calculations on addresses returned in DNS results to determine which port and IP address to use for command and control, rather than relying on a predetermined port number or the actual returned IP address. A IP and/or port number calculation can be used to bypass egress filtering on a C2 channel.(Citation: Meyers Numbered Panda)
One implementation of DNS Calculation is to take the first three octets of an IP address in a DNS response and use those values to calculate the port for command and control traffic.(Citation: Meyers Numbered Panda)(Citation: Moran 2014)(Citation: Rapid7G20Espionage)
View in MITRE ATT&CK®| Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name |
|---|---|---|---|---|
| action.malware.variety.C2 | Command and control (C2) | related-to | T1568.003 | Dynamic Resolution: DNS Calculation |