Certificate Request Export to Exchange Webserver — Sigma Rule

Rule metadata and linked tags

Author: Max Altgelt (Nextron Systems). Source status: test; severity: critical. Source dates: 2021-08-23 / 2023-01-23.

{
  "service": "msexchange-management",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 231164589966c7980323e9cc94bee77bbdf328c51f6bb4febcd4b1e4adadf60a

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: Certificate Request Export to Exchange Webserver
id: b7bc7038-638b-4ffd-880c-292c692209ef
status: test
description: Detects a write of an Exchange CSR to an untypical directory or with aspx name suffix which can be used to place a webshell
references:
    - https://twitter.com/GossiTheDog/status/1429175908905127938
author: Max Altgelt (Nextron Systems)
date: 2021-08-23
modified: 2023-01-23
tags:
    - attack.persistence
    - attack.t1505.003
logsource:
    service: msexchange-management
    product: windows
detection:
    keywords_export_command:
        '|all':
            - 'New-ExchangeCertificate'
            - ' -GenerateRequest'
            - ' -BinaryEncoded'
            - ' -RequestFile'
    keywords_export_params:
        - '\\\\localhost\\C$'
        - '\\\\127.0.0.1\\C$'
        - 'C:\\inetpub'
        - '.aspx'
    condition: keywords_export_command and keywords_export_params
falsepositives:
    - Unlikely
level: critical

Original YAML and metadata in JSON

False positives

• Unlikely

Source references

• https://twitter.com/GossiTheDog/status/1429175908905127938