Azure AD Unusual Number of Failed Authentications From Ip

name: Azure AD Unusual Number of Failed Authentications From Ip
id: 3d8d3a36-93b8-42d7-8d91-c5f24cec223d
version: 13
creation_date: '2022-07-11'
modification_date: '2026-05-13'
author: Mauricio Velazco, Gowthamaraj Rajendran, Splunk
status: production
type: Anomaly
description: The following analytic identifies a single source IP failing to authenticate with multiple valid users, potentially indicating a Password Spraying attack against an Azure Active Directory tenant. It uses Azure SignInLogs data and calculates the standard deviation for source IPs, applying the 3-sigma rule to detect unusual numbers of failed authentication attempts. This activity is significant as it may signal an adversary attempting to gain initial access or elevate privileges. If confirmed malicious, this could lead to unauthorized access, privilege escalation, and potential compromise of sensitive information.
data_source:
    - Azure Active Directory
search: |-
    `azure_monitor_aad` category=SignInLogs properties.status.errorCode=50126 properties.authenticationDetails{}.succeeded=false
      | rename properties.* as *
      | bucket span=5m _time
      | stats dc(userPrincipalName) AS unique_accounts values(userPrincipalName) as userPrincipalName values(dest) as dest  values(user) as user
        BY _time, src, vendor_account,
           vendor_product
      | eventstats avg(unique_accounts) as ip_avg, stdev(unique_accounts) as ip_std
        BY src
      | eval upperBound=(ip_avg+ip_std*3)
      | eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1,0)
      | where isOutlier = 1
      | `azure_ad_unusual_number_of_failed_authentications_from_ip_filter`
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 through an EventHub. This analytic was written to be used with the azure:monitor:aad sourcetype leveraging the Signin log category.
known_false_positives: A source Ip failing to authenticate with multiple users is not a common for legitimate behavior.
references:
    - https://attack.mitre.org/techniques/T1110/003/
    - https://docs.microsoft.com/en-us/security/compass/incident-response-playbook-password-spray
    - https://www.cisa.gov/uscert/ncas/alerts/aa21-008a
    - https://docs.microsoft.com/azure/active-directory/reports-monitoring/reference-sign-ins-error-codes
intermediate_findings:
    entities:
        - field: userPrincipalName
          type: user
          score: 20
          message: Possible Password Spraying attack against Azure AD from source ip $src$
threat_objects:
    - field: src
      type: ip_address
analytic_story:
    - Azure Active Directory Account Takeover
asset_type: Azure Active Directory
mitre_attack_id:
    - T1110.003
    - T1110.004
    - T1586.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: access