Exchange transport agent installation artifacts (PowerShell)

Status: experimental
Severity: high
Log source: category ['ps_module', 'ps_classic_script', 'ps_script'], product windows
Author: mdecrevoisier
Source: github.com/mdecrevoisier/SIGMA-detection-rules

Detects scenarios where an attacker attempts to load an artifact in the Exchange transport agent.

Known false positives

rare administrator change

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1505.002` Server Software Component: Transport Agent

Telemetry coverage

Provider	Record / event type
PowerShell	Event ID 4103: Payload Context: ContextInfo User Data: UserData.
PowerShell	Event ID 4104: Creating Scriptblock text (MessageNumber of MessageTotal).
PowerShell	Event ID 800

Rule body

title: Exchange transport agent installation artifacts (PowerShell)
description: Detects scenarios where an attacker attempts to load an artifact in the Exchange transport agent.
references:
- https://github.com/mdecrevoisier/EVTX-to-MITRE-Attack/tree/master/TA0003-Persistence/T1505-Server%20Software%20Component
- https://speakerdeck.com/heirhabarov/hunting-for-persistence-via-microsoft-exchange-server-or-outlook
- https://www.welivesecurity.com/wp-content/uploads/2019/05/ESET-LightNeuron.pdf
tags:
- attack.persistence
- attack.t1505.002 # Server Software Component: Transport Agent 
author: mdecrevoisier
status: experimental
logsource:
  product: windows
  category:
    - ps_module
    - ps_classic_script
    - ps_script
detection:
  selection_powershell_native:
    EventID: 800
    EventData|contains:
      - Enable-TransportAgent
      - Install-TransportAgent

  selection_powershell_modern:
    EventID: 4103
    Payload|contains:
      - Enable-TransportAgent
      - Install-TransportAgent

  selection_powershell_block:
    EventID: 4104
    ScriptBlockText|contains:
      - Enable-TransportAgent
      - Install-TransportAgent

  condition: 1 of selection*
falsepositives:
- rare administrator change
level: high

Stages and Predicates

Stage 0: `condition`

1 of selection*

Stage 1: `selection_powershell_native`

selection_powershell_native:
  EventID: 800
  EventData|contains:
    - Enable-TransportAgent
    - Install-TransportAgent

Stage 2: `selection_powershell_modern`

selection_powershell_modern:
  EventID: 4103
  Payload|contains:
    - Enable-TransportAgent
    - Install-TransportAgent

Stage 3: `selection_powershell_block`

selection_powershell_block:
  EventID: 4104
  ScriptBlockText|contains:
    - Enable-TransportAgent
    - Install-TransportAgent

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`EventData`	match	`Enable-TransportAgent` corpus 2 (sigma 2) `Install-TransportAgent` corpus 2 (sigma 2)	`field:"EventData" kind:match`
`Payload`	match	`Enable-TransportAgent` `Install-TransportAgent`	`field:"Payload" kind:match`
`ScriptBlockText`	match	`Enable-TransportAgent` `Install-TransportAgent`	`field:"ScriptBlockText" kind:match`

Exchange transport agent installation artifacts (PowerShell)

Known false positives

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_powershell_native

Stage 2: selection_powershell_modern

Stage 3: selection_powershell_block

Indicators

Stage 0: `condition`

Stage 1: `selection_powershell_native`

Stage 2: `selection_powershell_modern`

Stage 3: `selection_powershell_block`