Mailbox Export to Exchange Webserver — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems), Rich Warren, Christian Burkard (Nextron Systems). Source status: test; severity: critical. Source dates: 2021-08-09 / 2023-04-30.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 610c8a02a046035d0303872385ae81283234858effae7b0a563f7e374560f275

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: Mailbox Export to Exchange Webserver
id: 516376b4-05cd-4122-bae0-ad7641c38d48
status: test
description: Detects a successful export of an Exchange mailbox to untypical directory or with aspx name suffix which can be used to place a webshell or the needed role assignment for it
references:
    - https://blog.orange.tw/2021/08/proxylogon-a-new-attack-surface-on-ms-exchange-part-1.html
author: Florian Roth (Nextron Systems), Rich Warren, Christian Burkard (Nextron Systems)
date: 2021-08-09
modified: 2023-04-30
tags:
    - attack.persistence
    - attack.t1505.003
logsource:
    service: msexchange-management
    product: windows
detection:
    export_command:
        '|all':
            - 'New-MailboxExportRequest'
            - ' -Mailbox '
    export_params:
        - '-FilePath "\\\\' # We care about any share location.
        - '.aspx'
    role_assignment:
        '|all':
            - 'New-ManagementRoleAssignment'
            - ' -Role "Mailbox Import Export"'
            - ' -User '
    condition: (export_command and export_params) or role_assignment
falsepositives:
    - Unlikely
level: critical

Original YAML and metadata in JSON

False positives

• Unlikely

Source references

• https://blog.orange.tw/2021/08/proxylogon-a-new-attack-surface-on-ms-exchange-part-1.html