Outbound Network Connection Initiated By Cmstp.EXE — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2022-08-30 / 2024-05-31.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 2f068a8fa0a2c7d1f94ef7e9fc3c7ea71369330d986910f5746956c41b27a62f

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: Outbound Network Connection Initiated By Cmstp.EXE
id: efafe0bf-4238-479e-af8f-797bd3490d2d
status: test
description: |
    Detects a network connection initiated by Cmstp.EXE
    Its uncommon for "cmstp.exe" to initiate an outbound network connection. Investigate the source of such requests to determine if they are malicious.
references:
    - https://web.archive.org/web/20190720093911/http://www.endurant.io/cmstp/detecting-cmstp-enabled-code-execution-and-uac-bypass-with-sysmon/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-08-30
modified: 2024-05-31
tags:
    - attack.stealth
    - attack.t1218.003
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Image|endswith: '\cmstp.exe'
        Initiated: 'true'
    filter_main_local_ranges:
        DestinationIp|cidr:
            - '127.0.0.0/8'
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '169.254.0.0/16'
            - '::1/128'  # IPv6 loopback
            - 'fe80::/10'  # IPv6 link-local addresses
            - 'fc00::/7'  # IPv6 private addresses
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
# Note: Please report any false positive seen in the wild to help tune the rule.
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://web.archive.org/web/20190720093911/http://www.endurant.io/cmstp/detecting-cmstp-enabled-code-execution-and-uac-bypass-with-sysmon/