Detection rules › Splunk
O365 High Number Of Failed Authentications for User
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.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Credential Access | T1110.001 Brute Force: Password Guessing |
Rules detecting the same action
Other rules on this platform that filter on the same API call or operation.
- High Number of Login Failures from a single source (Splunk)
- M365 Identity User Account Lockouts (Elastic)
- M365 Identity User Brute Force Attempted (Elastic)
- O365 Excessive SSO logon errors (Splunk)
- O365 Multi-Source Failed Authentications Spike (Splunk)
- O365 Multiple AppIDs and UserAgents Authentication Spike (Splunk)
- O365 Multiple Failed MFA Requests For User (Splunk)
- O365 Multiple Users Failing To Authenticate From Ip (Splunk)
Rule body splunk
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
Stages and Predicates
Stage 1: search
`o365_management_activity` Operation=UserLoginFailed record_type=AzureActiveDirectoryStsLogon Workload=AzureActiveDirectory
Stage 2: bucket
| bucket span=5m _time
Stage 3: fillnull
| fillnull
Stage 4: stats
| stats dc(_raw) AS failed_attempts values(src_ip) as src
BY signature user _time
dest vendor_account vendor_product
Stage 5: where
| where failed_attempts > 10
Stage 6: search
| `o365_high_number_of_failed_authentications_for_user_filter`
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
Operation | eq |
|
Workload | eq |
|
failed_attempts | gt |
|
record_type | eq |
|
sourcetype | eq |
|