O365 High Number Of Failed Authentications for User

SPLUNK detection rule by Mauricio Velazco, Splunk · Apache-2.0

The following analytic identifies an O365 account experiencing more than 20 failed authentication attempts within 5 minutes. It uses O365 Unified Audit Logs, specifically "UserLoginFailed" events, to monitor and flag accounts exceeding this threshold. This activity is significant as it may indicate a brute force attack or password guessing attempt. If confirmed malicious, an attacker could gain unauthorized access to the O365 environment, potentially compromising sensitive emails, documents, and other data. Prompt investigation and action are crucial to prevent unauthorized access and data breaches.

name: O365 High Number Of Failed Authentications for User
id: 31641378-2fa9-42b1-948e-25e281cb98f7
version: 12
creation_date: '2023-12-06'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic identifies an O365 account experiencing more than 20 failed authentication attempts within 5 minutes. It uses O365 Unified Audit Logs, specifically "UserLoginFailed" events, to monitor and flag accounts exceeding this threshold. This activity is significant as it may indicate a brute force attack or password guessing attempt. If confirmed malicious, an attacker could gain unauthorized access to the O365 environment, potentially compromising sensitive emails, documents, and other data. Prompt investigation and action are crucial to prevent unauthorized access and data breaches.
data_source:
    - O365 UserLoginFailed
search: |-
    `o365_management_activity` Operation=UserLoginFailed record_type=AzureActiveDirectoryStsLogon Workload=AzureActiveDirectory
      | bucket span=5m _time
      | fillnull
      | stats dc(_raw) AS failed_attempts values(src_ip) as src
        BY signature user _time
           dest vendor_account vendor_product
      | where failed_attempts > 10
      | `o365_high_number_of_failed_authentications_for_user_filter`
how_to_implement: You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
known_false_positives: Although unusual, users who have lost their passwords may trigger this detection. Filter as needed.
references:
    - https://attack.mitre.org/techniques/T1110/
    - https://attack.mitre.org/techniques/T1110/001/
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"
finding:
    title: User $user$ failed to authenticate more than 10 times in the span of 5 minutes.
    entity:
        field: user
        type: user
        score: 50
threat_objects:
    - field: src
      type: ip_address
analytic_story:
    - Office 365 Account Takeover
asset_type: O365 Tenant
mitre_attack_id:
    - T1110.001
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: identity
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1110.001/o365_high_number_authentications_for_user/o365_high_number_authentications_for_user.log
          source: o365:management:activity
          sourcetype: o365:management:activity
      test_type: unit

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

6199c43d-3f88-4f05-a4bb-e7d17ca24dad

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