Detection: O365 Excessive Authentication Failures Alert

Updated Date: 2024-05-18 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.

Search

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

Name	Platform	Sourcetype	Source	Supported App
N/A	N/A	N/A	N/A	N/A

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

DarkVishnya

Dragonfly

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

Office 365 Account Takeover

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

https://attack.mitre.org/techniques/T1110/

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: 3