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Description

The following analytic identifies multiple failed multi-factor authentication requests for a single user within an Azure AD tenant. Error Code 500121 represents a failed attempt to authenticate using a second factor. Specifically, the analytic triggers when more than 10 MFA user prompts fail within 10 minutes. Azure AD tenants can be very different depending on the organization, Security teams should test this detection and customize these arbitrary thresholds. The detected behavior may represent an adversary who has obtained legitimate credentials for a user and continuously repeats login attempts in order to bombard users with MFA push notifications, SMS messages, and phone calls potentially resulting in the user finally accepting the authentication request. Threat actors like the Lapsus team and APT29 have leveraged this technique to bypass multi-factor authentication controls as reported by Mandiant and others.

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

  • Last Updated: 2022-08-25
  • Author: Mauricio Velazco, Splunk
  • ID: 264ea131-ab1f-41b8-90e0-33ad1a1888ea

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1621 Multi-Factor Authentication Request Generation Credential Access
T1078 Valid Accounts Defense Evasion, Persistence, Privilege Escalation, Initial Access
T1078.004 Cloud Accounts Defense Evasion, Persistence, Privilege Escalation, Initial Access
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 3
  • CIS 5
  • CIS 16
CVE
1
2
3
4
5
6
 `azuread` body.category=SignInLogs body.properties.status.errorCode=500121 
| rename body.properties.* as * 
| bucket span=10m _time 
| stats dc(_raw) AS mfa_prompts values(userPrincipalName) by userPrincipalName, status.additionalDetails, appDisplayName, userAgent, _time 
| where mfa_prompts > 10 
| `azure_ad_multiple_failed_mfa_requests_for_user_filter`

Macros

The SPL above uses the following Macros:

:information_source: azure_ad_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
  • body.properties.status.errorCode
  • body.category
  • body.properties.authenticationDetails
  • body.properties.userPrincipalName
  • body.properties.ipAddress

How To Implement

You must install the latest version of Splunk Add-on for Microsoft Cloud Services from Splunkbase (https://splunkbase.splunk.com/app/3110/#/details). You must be ingesting Azure Active Directory events into your Splunk environment. Specifically, this analytic leverages the SignInLogs log category.

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
63.0 70 90 Multiple Failed MFA requests for user $body.properties.userPrincipalName$

: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

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