Detection rules › Sigma

DLL Loaded From Suspicious Location Via Cmspt.EXE

Status
test
Severity
high
Log source
category image_load, product windows
Author
Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects cmstp loading "dll" or "ocx" files from suspicious locations

Known false positives

  • Unikely

MITRE ATT&CK coverage

Telemetry coverage

ProviderRecord / event type
SysmonEvent ID 7: Image loaded

Rule body

title: DLL Loaded From Suspicious Location Via Cmspt.EXE
id: 75e508f7-932d-4ebc-af77-269237a84ce1
status: test
description: Detects cmstp loading "dll" or "ocx" files from suspicious locations
references:
    - https://github.com/vadim-hunter/Detection-Ideas-Rules/blob/02bcbfc2bfb8b4da601bb30de0344ae453aa1afe/TTPs/Defense%20Evasion/T1218%20-%20Signed%20Binary%20Proxy%20Execution/T1218.003%20-%20CMSTP/Procedures.yaml
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-08-30
modified: 2023-02-17
tags:
    - attack.stealth
    - attack.t1218.003
logsource:
    category: image_load
    product: windows
detection:
    selection:
        Image|endswith: '\cmstp.exe'
        ImageLoaded|contains:
            # Add more suspicious paths as you see fit in your env
            - '\PerfLogs\'
            - '\ProgramData\'
            - '\Users\'
            - '\Windows\Temp\'
            - 'C:\Temp\'
        ImageLoaded|endswith:
            - '.dll'
            - '.ocx'
    condition: selection
falsepositives:
    - Unikely
level: high

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    Image|endswith: '\cmstp.exe'
    ImageLoaded|contains:
        - '\PerfLogs\'
        - '\ProgramData\'
        - '\Users\'
        - '\Windows\Temp\'
        - 'C:\Temp\'
    ImageLoaded|endswith:
        - '.dll'
        - '.ocx'

Indicators

These rows show field, operator, and value matches.

FieldKindValuesSearch
Imageends_with
  • \cmstp.exe corpus 8 (sigma 8)
field:"Image" kind:ends_with value:"\cmstp.exe"
ImageLoadedends_with
  • .dll corpus 6 (sigma 3, splunk 3)
  • .ocx
field:"ImageLoaded" kind:ends_with
ImageLoadedmatch
  • C:\Temp\
  • \PerfLogs\ corpus 2 (sigma 2)
  • \ProgramData\ corpus 2 (sigma 2)
  • \Users\
  • \Windows\Temp\ corpus 2 (sigma 2)
field:"ImageLoaded" kind:match