Detection: O365 Multiple OS Vendors Authenticating From User

Updated Date: 2024-12-19 ID: 3451e58a-9457-4985-a600-b616b0cbfda1 Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies when multiple operating systems are used to authenticate to Azure/EntraID/Office 365 by the same user account over a short period of time. This activity could be indicative of attackers enumerating various logon capabilities of Azure/EntraID/Office 365 and attempting to discover weaknesses in the organizational MFA or conditional access configurations. Usage of the tools like "MFASweep" will trigger this detection.

Search

 1`o365_management_activity` Operation IN (UserLoginFailed,UserLoggedIn)
 2
 3| eval -time = _time
 4
 5| bin _time span=15m
 6
 7| stats values(Operation) as signature, values(ErrorNumber) as signature_id, values(OS) as os_name, dc(OS) as os_count, count, min(-time) as firstTime, max(-time) as lastTime by  ClientIP, UserId, _time
 8
 9| where os_count >= 4
10
11| eval src = ClientIP, user = UserId
12
13| `security_content_ctime(firstTime)` 
14
15| `security_content_ctime(lastTime)`
16
17| `o365_multiple_os_vendors_authenticating_from_user_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name	Value
o365_management_activity	`sourcetype=o365:management:activity`
o365_multiple_os_vendors_authenticating_from_user_filter	`search *`

o365_multiple_os_vendors_authenticating_from_user_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1110	Brute Force	Credential Access

Exploitation

DE.CM

CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events. The thresholds set within the analytic (such as unique OS) are initial guidelines and should be customized based on the organization's user behavior and risk profile. Security teams are encouraged to adjust these thresholds to optimize the balance between detecting genuine threats and minimizing false positives, ensuring the detection is tailored to their specific environment.

Known False Positives

IP or users where the usage of multiple Operating systems is expected, filter accordingly.

Associated Analytic Story

Office 365 Account Takeover

Risk Based Analytics (RBA)

Risk Message:

The user account $user$ authenticated with $os_count$ unique operating system types over a short period from $src$.

Risk Object	Risk Object Type	Risk Score	Threat Objects
user	user	60	src

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`o365`	`o365:management:activity`
Integration	✅ Passing	Dataset	`o365`	`o365:management:activity`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1