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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.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-05-26
  • Author: Mauricio Velazco, Splunk
  • ID: fd22124e-dbac-4744-a8ce-be10d8ec3e26

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1621 Multi-Factor Authentication Request Generation Credential Access
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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

Macros

The SPL above uses the following Macros:

:information_source: o365_multiple_failed_mfa_requests_for_user_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • Workload
  • Operation
  • ResultStatus
  • ErrorNumber
  • user
  • LogonError
  • signature

How To Implement

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

RBA

Risk Score Impact Confidence Message
48.0 60 80 Multiple failed MFA requestes for $user$

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

Reference

Test Dataset

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 | version: 2