Suspicious Serv-U Process Pattern — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2021-07-14 / 2022-07-14.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 8edee94416b267656e8a9575b219129aeb073d1756a283f1b39a91125e7547d1

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: Suspicious Serv-U Process Pattern
id: 58f4ea09-0fc2-4520-ba18-b85c540b0eaf
status: test
description: Detects a suspicious process pattern which could be a sign of an exploited Serv-U service
references:
    - https://www.microsoft.com/security/blog/2021/07/13/microsoft-discovers-threat-actor-targeting-solarwinds-serv-u-software-with-0-day-exploit/
author: Florian Roth (Nextron Systems)
date: 2021-07-14
modified: 2022-07-14
tags:
    - attack.credential-access
    - attack.t1555
    - cve.2021-35211
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\Serv-U.exe'
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
            - '\pwsh.exe'
            - '\wscript.exe'
            - '\cscript.exe'
            - '\sh.exe'
            - '\bash.exe'
            - '\schtasks.exe'
            - '\regsvr32.exe'
            - '\wmic.exe'  # https://app.any.run/tasks/c903e9c8-0350-440c-8688-3881b556b8e0/
            - '\mshta.exe'
            - '\rundll32.exe'
            - '\msiexec.exe'
            - '\forfiles.exe'
            - '\scriptrunner.exe'
    condition: selection
falsepositives:
    - Legitimate uses in which users or programs use the SSH service of Serv-U for remote command execution
level: high

Original YAML and metadata in JSON

False positives

• Legitimate uses in which users or programs use the SSH service of Serv-U for remote command execution

Source references

• https://www.microsoft.com/security/blog/2021/07/13/microsoft-discovers-threat-actor-targeting-solarwinds-serv-u-software-with-0-day-exploit/