Testing Usage of Uncommonly Used Port — Sigma Rule

Rule metadata and linked tags

Author: frack113. Source status: test; severity: medium. Source dates: 2022-01-23 / not supplied.

{
  "product": "windows",
  "category": "ps_script",
  "definition": "Requirements: Script Block Logging must be enabled"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 8febac78f91b06c8296e3aee6afd31107533dac0c7017935b1d0b226a174f93c

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Testing Usage of Uncommonly Used Port
id: adf876b3-f1f8-4aa9-a4e4-a64106feec06
status: test
description: |
    Adversaries may communicate using a protocol and port paring that are typically not associated.
    For example, HTTPS over port 8088(Citation: Symantec Elfin Mar 2019) or port 587(Citation: Fortinet Agent Tesla April 2018) as opposed to the traditional port 443.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1571/T1571.md#atomic-test-1---testing-usage-of-uncommonly-used-port-with-powershell
    - https://learn.microsoft.com/en-us/powershell/module/nettcpip/test-netconnection?view=windowsserver2022-ps
author: frack113
date: 2022-01-23
tags:
    - attack.command-and-control
    - attack.t1571
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        ScriptBlockText|contains|all:
            - Test-NetConnection
            - '-ComputerName '
            - '-port '
    filter:
        ScriptBlockText|contains:
            - ' 443 '
            - ' 80 '
    condition: selection and not filter
falsepositives:
    - Legitimate administrative script
level: medium

Original YAML and metadata in JSON

False positives

• Legitimate administrative script

Source references

• https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1571/T1571.md#atomic-test-1---testing-usage-of-uncommonly-used-port-with-powershell
• https://learn.microsoft.com/en-us/powershell/module/nettcpip/test-netconnection?view=windowsserver2022-ps