Privileged User Has Been Created — Sigma Rule

Rule metadata and linked tags

Author: Pawel Mazur. Source status: test; severity: high. Source dates: 2022-12-21 / 2025-01-21.

{
  "product": "linux",
  "definition": "/var/log/secure on REHL systems or /var/log/auth.log on debian like Systems needs to be collected in order for this detection to work"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: d3077e7863686f8da3428c8b3d5ab819648fc0dbeead29ac1792ab138a28f967

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: Privileged User Has Been Created
id: 0ac15ec3-d24f-4246-aa2a-3077bb1cf90e
status: test
description: Detects the addition of a new user to a privileged group such as "root" or "sudo"
references:
    - https://digital.nhs.uk/cyber-alerts/2018/cc-2825
    - https://linux.die.net/man/8/useradd
    - https://github.com/redcanaryco/atomic-red-team/blob/25acadc0b43a07125a8a5b599b28bbc1a91ffb06/atomics/T1136.001/T1136.001.md#atomic-test-5---create-a-new-user-in-linux-with-root-uid-and-gid
author: Pawel Mazur
date: 2022-12-21
modified: 2025-01-21
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1136.001
    - attack.t1098
logsource:
    product: linux
    definition: '/var/log/secure on REHL systems or /var/log/auth.log on debian like Systems needs to be collected in order for this detection to work'
detection:
    # Example of the events that could be observed when matching these would be as follow
    #   Dec 21 16:42:19 testserver useradd[1337]: new user: name=butter1, UID=1000, GID=0, home=/root, shell=/bin/bash
    #   Dec 21 17:13:54 testserver useradd[1337]: new user: name=john, UID=0, GID=0, home=/home/john, shell=/bin/bash
    #   Dec 21 17:24:40 testserver useradd[1337]: new user: name=butter3, UID=1000, GID=10, home=/home/butter3, shell=/bin/bash
    #   Dec 21 17:30:22 testserver useradd[1337]: new user: name=butter4, UID=1000, GID=27, home=/home/butter4, shell=/bin/bash
    selection_new_user:
        - 'new user'
    selection_uids_gids:
        - 'GID=0,' # root group
        - 'UID=0,' # root UID
        - 'GID=10,' # wheel group
        - 'GID=27,' # sudo group
    condition: all of selection_*
falsepositives:
    - Administrative activity
level: high

Original YAML and metadata in JSON

False positives

• Administrative activity

Source references

• https://digital.nhs.uk/cyber-alerts/2018/cc-2825
• https://linux.die.net/man/8/useradd
• https://github.com/redcanaryco/atomic-red-team/blob/25acadc0b43a07125a8a5b599b28bbc1a91ffb06/atomics/T1136.001/T1136.001.md#atomic-test-5---create-a-new-user-in-linux-with-root-uid-and-gid