O365 Excessive Authentication Failures Alert

SPLUNK detection rule by Rod Soto, Splunk · Apache-2.0

The following analytic identifies an excessive number of authentication failures, including failed attempts against MFA prompt codes. It uses data from the `o365_management_activity` dataset, focusing on events where the authentication status is marked as failure. This behavior is significant as it may indicate a brute force attack or an attempt to compromise user accounts. If confirmed malicious, this activity could lead to unauthorized access, data breaches, or further exploitation within the environment.

name: O365 Excessive Authentication Failures Alert
id: d441364c-349c-453b-b55f-12eccab67cf9
version: 11
creation_date: '2020-12-16'
modification_date: '2026-05-13'
author: Rod Soto, Splunk
status: production
type: Anomaly
description: The following analytic identifies an excessive number of authentication failures, including failed attempts against MFA prompt codes. It uses data from the `o365_management_activity` dataset, focusing on events where the authentication status is marked as failure. This behavior is significant as it may indicate a brute force attack or an attempt to compromise user accounts. If confirmed malicious, this activity could lead to unauthorized access, data breaches, or further exploitation within the environment.
data_source: []
search: |-
    `o365_management_activity` Workload=AzureActiveDirectory UserAuthenticationMethod=* status=failure
      | stats count earliest(_time) AS firstTime latest(_time) AS lastTime values(UserAuthenticationMethod) AS UserAuthenticationMethod values(UserAgent) AS user_agent values(status) AS status values(src_ip) AS src values(signature) as signature
        BY user vendor_account vendor_product
           dest
      | where count > 10
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `o365_excessive_authentication_failures_alert_filter`
how_to_implement: You must install splunk Microsoft Office 365 add-on. This search works with o365:management:activity
known_false_positives: The threshold for alert is above 10 attempts and this should reduce the number of false positives.
references:
    - https://attack.mitre.org/techniques/T1110/
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: user
          type: user
          score: 20
          message: User $user$ has caused excessive number of authentication failures from $src$ using UserAgent $user_agent$.
threat_objects:
    - field: src
      type: ip_address
analytic_story:
    - Office 365 Account Takeover
asset_type: O365 Tenant
mitre_attack_id:
    - T1110
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: threat
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1110/o365_brute_force_login/o365_brute_force_login.json
          sourcetype: o365:management:activity
          source: o365
      test_type: unit

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