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Detection rules › Sigma

Suspicious Serv-U Process Pattern

Status
test
Severity
high
Log source
product windows, category process_creation
Author
Florian Roth (Nextron Systems)
Source
github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

TacticTechniques
Credential AccessT1555 Credentials from Password Stores

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

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

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

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'
        - '\mshta.exe'
        - '\rundll32.exe'
        - '\msiexec.exe'
        - '\forfiles.exe'
        - '\scriptrunner.exe'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
Imageends_with
  • \bash.exe corpus 22 (sigma 22)
  • \cmd.exe corpus 130 (sigma 130)
  • \cscript.exe corpus 73 (sigma 73)
  • \forfiles.exe corpus 12 (sigma 12)
  • \mshta.exe corpus 67 (sigma 67)
  • \msiexec.exe corpus 21 (sigma 21)
  • \powershell.exe corpus 182 (sigma 182)
  • \pwsh.exe corpus 168 (sigma 168)
  • \regsvr32.exe corpus 65 (sigma 65)
  • \rundll32.exe corpus 95 (sigma 95)
  • \schtasks.exe corpus 56 (sigma 56)
  • \scriptrunner.exe corpus 12 (sigma 12)
  • \sh.exe corpus 16 (sigma 16)
  • \wmic.exe corpus 60 (sigma 60)
  • \wscript.exe corpus 75 (sigma 75)
ParentImageends_with
  • \Serv-U.exe