Suspicious Serv-U Process Pattern

SIGMA detection rule by Florian Roth (Nextron Systems) · GPL-2.0

Detects a suspicious process pattern which could be a sign of an exploited Serv-U service

title: Suspicious Serv-U Process Pattern
id: 83e16972-fa32-9c0e-e39d-25254c56a9ff
related:
    - id: 58f4ea09-0fc2-4520-ba18-b85c540b0eaf
      type: derived
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:
    process_creation:
        EventID: 4688
        Channel: Security
    selection:
        ParentProcessName|endswith: \Serv-U.exe
        NewProcessName|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: process_creation and selection
falsepositives:
    - Legitimate uses in which users or programs use the SSH service of Serv-U for remote command execution
level: high
ruletype: Sigma

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

dd9f6112-fd8c-4fbf-b566-3e4de464a512

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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