The following analytic identifies an authentication attempt event against an Azure AD tenant that fails during the Multi Factor Authentication challenge. This behavior may represent an adversary trying to authenticate with compromised credentials. In some cases, adversaries may continuously repeat 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.
- Type: TTP
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2022-07-14
- Author: Mauricio Velazco, Splunk
- ID: e62c9c2e-bf51-4719-906c-3074618fcc1c
Kill Chain Phase
- CIS 3
- CIS 5
- CIS 16
1 2 3 4 `azuread` body.category=SignInLogs body.properties.status.errorCode=500121 | rename body.properties.* as * | stats values(userPrincipalName) by _time, ipAddress, status.additionalDetails, appDisplayName, userAgent | `azure_ad_authentication_failed_during_mfa_challenge_filter`
The SPL above uses the following Macros:
azure_ad_authentication_failed_during_mfa_challenge_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
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. You must be ingesting Azure Active Directory events in your Splunk environment. Specifically, this analytic leverages the RiskyUsers and UserRiskEvents log category.
Known False Positives
Legitimate users may miss to reply the MFA challenge within the time window or deny it by mistake.
Associated Analytic Story
|54.0||60||90||User $body.properties.userPrincipalName$ failed to pass MFA challenge|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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