Modify Exchange Access Settings (PowerShell)

Group by: _time, host
Source: github.com/anvilogic-forge/armory

Set-CASMailbox cmdlet to configure client access settings on a mailbox. For example, you can configure settings for Exchange ActiveSync, Outlook, Outlook on the web, POP3, and IMAP4. Attacker added their own devices as allowed IDs for active sync

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

References

https://www.volexity.com/blog/2020/12/14/dark-halo-leverages-solarwinds-compromise-to-breach-organizations/

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).

Rule body

id: '5696.5958'
title: Modify Exchange Access Settings
description: 'Set-CASMailbox cmdlet to configure client access settings on a mailbox.
  For example, you can configure settings for Exchange ActiveSync, Outlook, Outlook
  on the web, POP3, and IMAP4. Attacker added their own devices as allowed IDs for
  active sync. - Threat Actor Association: APT29/Nobelium/Cozy Bear'
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4104) OR
  TERM(EventCode=4103)) TERM(Set-CASMailbox) | table _time, host, user signature_id,
  process, process_* `group_events("host",1s)` '
techniques:
- execution:command and scripting interpreter:powershell
technique_id:
- T1059.001
data_category:
- PowerShell logs
- Process command-line parameters
references:
- https://www.volexity.com/blog/2020/12/14/dark-halo-leverages-solarwinds-compromise-to-breach-organizations/

Stages and Predicates

Stage 1: `search`

search EventCode=4103 EventCode=4104 source="*" source IN ("WinEventLog:Microsoft-Windows-PowerShell/Operational", "WinEventLog:Windows", "XmlWinEventLog:Microsoft-Windows-PowerShell/Operational")

Stage 2: `table`

table _time, host, process, process_*, signature_id, user

Stage 3: `bucket`

bucket _time

Stage 4: `stats`

stats BY host, _time

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`EventCode`	eq	`4103` corpus 105 (splunk 105) `4104` corpus 269 (splunk 269)	`field:"EventID" kind:eq`

Search terms

These SPL tokens match against raw event text.

Stage	Term
1	`"Set-CASMailbox"`