# T1568.003_dns-calculation

> 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 o...

- Skill: `cyberstrikeus/t1568-003-dns-calculation` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/t1568-003-dns-calculation`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/t1568-003-dns-calculation/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/t1568-003-dns-calculation

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# T1568.003 DNS Calculation

> **Sub-technique of:** T1568

## High-Level Description

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.

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.

## Kill Chain Phase

- Command and Control (TA0011)

**Platforms:** Linux, macOS, Windows, ESXi

## What to Check

- [ ] Identify if DNS Calculation technique is applicable to target environment
- [ ] Check Linux systems for indicators of DNS Calculation
- [ ] Check macOS systems for indicators of DNS Calculation
- [ ] Check Windows systems for indicators of DNS Calculation
- [ ] Assess detection coverage (1 detection strategies)

## How to Test

### Manual Testing

1. **Identify Attack Surface**: Determine if the target environment is susceptible to DNS Calculation by examining the target platforms (Linux, macOS, Windows).

2. **Assess Existing Defenses**: Review whether mitigations for T1568.003 are in place. If defenses are absent or misconfigured, this technique may be exploitable.

3. **Execute Test**: Use tools and methods described in the MITRE ATT&CK page and external references below.

> **Note**: No Atomic Red Team tests available for this technique. See [Atomic Red Team GitHub](https://github.com/redcanaryco/atomic-red-team) for updates.

## Remediation Guide

No specific mitigations documented for this technique.

## Detection

### Detection Strategy for Dynamic Resolution through DNS Calculation

## Risk Assessment

| Finding                              | Severity | Impact              |
| ------------------------------------ | -------- | ------------------- |
| DNS Calculation technique applicable | Low      | Command And Control |

## CWE Categories

| CWE ID  | Title                              |
| ------- | ---------------------------------- |
| CWE-300 | Channel Accessible by Non-Endpoint |

## References

- [Meyers Numbered Panda](http://www.crowdstrike.com/blog/whois-numbered-panda/)
- [Moran 2014](https://www.fireeye.com/blog/threat-research/2014/09/darwins-favorite-apt-group-2.html)
- [Rapid7G20Espionage](https://blog.rapid7.com/2013/08/26/upcoming-g20-summit-fuels-espionage-operations/)
- [Atomic Red Team - T1568.003](https://github.com/redcanaryco/atomic-red-team/tree/master/atomics/T1568.003)
- [MITRE ATT&CK - T1568.003](https://attack.mitre.org/techniques/T1568/003)