Detection: O365 Excessive Authentication Failures Alert

Updated Date: 2024-09-30 ID: d441364c-349c-453b-b55f-12eccab67cf9 Author: Rod Soto, Splunk Type: Anomaly Product: Splunk Enterprise Security

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.

1`o365_management_activity` Workload=AzureActiveDirectory UserAuthenticationMethod=* status=failure 
2| stats count earliest(_time) AS firstTime latest(_time) AS lastTime values(UserAuthenticationMethod) AS UserAuthenticationMethod values(UserAgent) AS UserAgent values(status) AS status values(src_ip) AS src_ip by user 
3| where count > 10 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `o365_excessive_authentication_failures_alert_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name Value
o365_management_activity sourcetype=o365:management:activity
o365_excessive_authentication_failures_alert_filter search *
o365_excessive_authentication_failures_alert_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1110 Brute Force Credential Access
KillChainPhase.EXPLOITAITON
NistCategory.DE_AE
Cis18Value.CIS_10
APT28
APT38
APT39
APT41
Agrius
DarkVishnya
Dragonfly
Ember Bear
FIN5
Fox Kitten
HEXANE
OilRig
Turla

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

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.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
User $user$ has caused excessive number of authentication failures from $src_ip$ using UserAgent $UserAgent$. 64 80 80
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset o365 o365:management:activity
Integration ✅ Passing Dataset o365 o365:management:activity

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 4