PUA - NimScan Execution — Sigma Rule

Rule metadata and linked tags

Author: Swachchhanda Shrawan Poudel (Nextron Systems). Source status: test; severity: medium. Source dates: 2025-02-05 / not supplied.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 34e278c5e19e758dc2b4db440a7f1f8764ee6b8e853b649b89bbec9e4e7c550e

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: PUA - NimScan Execution
id: 4fd6b1c7-19b8-4488-97f6-00f0924991a3
status: test
description: |
    Detects usage of NimScan, a portscanner utility.
    In early 2025, adversaries were observed using this utility to scan for open ports on remote hosts in a compromised environment.
    This rule identifies the execution of NimScan based on the process image name and specific hash values associated with different versions of the tool.
references:
    - https://x.com/cyberfeeddigest/status/1887041526397587859
    - https://github.com/elddy/NimScan
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-02-05
tags:
    - attack.discovery
    - attack.t1046
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - Image|endswith: '\NimScan.exe' # Other metadata fields such as originalfilename and product were omitted because they were null
        - Hashes|contains:
              - 'IMPHASH=41BB1C7571B3A724EB83A1D2B96DBB8C' # v1.0.8
              - 'IMPHASH=B1B6ADACB172795480179EFD18A29549' # v1.0.6
              - 'IMPHASH=0D1F896DC7642AD8384F9042F30279C2' # v1.0.4 and v1.0.2
    condition: selection
falsepositives:
    - Legitimate administrator activity
level: medium

Original YAML and metadata in JSON

False positives

• Legitimate administrator activity

Source references

• https://x.com/cyberfeeddigest/status/1887041526397587859
• https://github.com/elddy/NimScan