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Detection rules › Sigma

Mailbox Export to Exchange Webserver

Status
test
Severity
critical
Log source
product windows, service msexchange-management
Author
Florian Roth (Nextron Systems), Rich Warren, Christian Burkard (Nextron Systems)
Source
github.com/SigmaHQ/sigma

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

Known false positives

  • Unlikely

MITRE ATT&CK coverage

TacticTechniques
Persistence

Rule body

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

Stages and Predicates

Stage 0: condition

(export_command and export_params) or role_assignment

Stage 1: export_command

export_command:
    '|all':
        - 'New-MailboxExportRequest'
        - ' -Mailbox '

Stage 2: export_params

export_params:
    - '-FilePath "\\\\'
    - '.aspx'

Stage 3: role_assignment

role_assignment:
    '|all':
        - 'New-ManagementRoleAssignment'
        - ' -Role "Mailbox Import Export"'
        - ' -User '