Detection rules › Splunk
Modify Exchange Access Settings (PowerShell)
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
Event coverage
| Provider | Event | Title |
|---|---|---|
| PowerShell | Event ID 4103 | Payload Context: ContextInfo User Data: UserData. |
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Rule body yaml
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
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
EventCode | eq |
|
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | TERM |
| 1 | "Set-CASMailbox" |