Detection: O365 Multiple Failed MFA Requests For User

Updated Date: 2024-09-30 ID: fd22124e-dbac-4744-a8ce-be10d8ec3e26 Author: Mauricio Velazco, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies potential "MFA fatigue" attacks targeting Office 365 users by detecting more than nine Multi-Factor Authentication (MFA) prompts within a 10-minute timeframe. It leverages O365 management activity logs, focusing on Azure Active Directory events with the UserLoginFailed operation, a Success ResultStatus, and an ErrorNumber of 500121. This activity is significant as attackers may exploit MFA fatigue to gain unauthorized access by overwhelming users with repeated MFA requests. If confirmed malicious, this could lead to data breaches, unauthorized data access, or further compromise within the O365 environment. Immediate investigation is crucial.

Search

1`o365_management_activity` Workload=AzureActiveDirectory Operation=UserLoginFailed ResultStatus=Success  ErrorNumber=500121 
2| bucket span=10m _time 
3| stats  dc(_raw) as mfa_prompts values(LogonError) as LogonError values(signature) as signature by user, _time 
4| where  mfa_prompts  > 9 
5| `o365_multiple_failed_mfa_requests_for_user_filter`

Data Source

Name	Platform	Sourcetype	Source
O365 UserLoginFailed	N/A	`'o365:management:activity'`	`'o365'`

Macros Used

Name	Value
o365_management_activity	`sourcetype=o365:management:activity`
o365_multiple_failed_mfa_requests_for_user_filter	`search *`

o365_multiple_failed_mfa_requests_for_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
T1621	Multi-Factor Authentication Request Generation	Credential Access

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT29

LAPSUS$

Scattered Spider

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.

Known False Positives

Multiple Failed MFA requests may also be a sign of authentication or application issues. Filter as needed.

Associated Analytic Story

Office 365 Account Takeover

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Multiple failed MFA requestes for $user$	48	60	80

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

https://attack.mitre.org/techniques/T1621/

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: 4