Detection: AWS Unusual Number of Failed Authentications From Ip

Updated Date: 2025-03-27 ID: 0b5c9c2b-e2cb-4831-b4f1-af125ceb1386 Author: Bhavin Patel, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies a single source IP failing to authenticate into the AWS Console with multiple valid users. It uses CloudTrail logs and calculates the standard deviation for source IP, leveraging the 3-sigma rule to detect unusual numbers of failed authentication attempts. This behavior is significant as it may indicate a Password Spraying attack, where an adversary attempts to gain initial access or elevate privileges. If confirmed malicious, this activity could lead to unauthorized access, data breaches, or further exploitation within the AWS environment.

Search

 1`cloudtrail` eventName=ConsoleLogin action=failure 
 2| rename eventName as action, eventSource as dest, userName as user, userAgent as user_agent, sourceIPAddress as src, userIdentity.accountId as vendor_account, awsRegion as vendor_region 
 3| bucket span=10m _time 
 4| stats  dc(_raw) AS distinct_attempts values(user_name) as tried_accounts values(action) as action values(dest) as dest values(vendor_account) as vendor_account values(vendor_region) as vendor_region values(vendor_product) as vendor_product values(user_agent) as user_agent by _time, src 
 5| eventstats avg(distinct_attempts) as avg_attempts , stdev(distinct_attempts) as ip_std by _time 
 6| eval upperBound=(avg_attempts+ip_std*3) 
 7| eval  isOutlier=if(distinct_attempts > 10 and distinct_attempts >= upperBound, 1, 0) 
 8| where isOutlier = 1 
 9| `security_content_ctime(firstTime)` 
10| `security_content_ctime(lastTime)` 
11| `aws_unusual_number_of_failed_authentications_from_ip_filter`

Data Source

Name	Platform	Sourcetype	Source
AWS CloudTrail ConsoleLogin	AWS	`'aws:cloudtrail'`	`'aws_cloudtrail'`

Macros Used

Name	Value
cloudtrail	`sourcetype=aws:cloudtrail`
aws_unusual_number_of_failed_authentications_from_ip_filter	`search *`

aws_unusual_number_of_failed_authentications_from_ip_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
T1110.003	Password Spraying	Credential Access
T1110.004	Credential Stuffing	Credential Access
T1586.003	Cloud Accounts	Resource Development

Exploitation

Weaponization

DE.AE

CIS 10

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 Add-on for AWS in order to ingest Cloudtrail. We recommend the users to try different combinations of the bucket span time and the calculation of the upperBound field to tune this search according to their environment

Known False Positives

No known false postives for this detection. Please review this alert

Associated Analytic Story

AWS Identity and Access Management Account Takeover

Risk Based Analytics (RBA)

Risk Message:

Unusual number of failed console login attempts (Count: $distinct_attempts$) against users from IP Address - $src$

Risk Object	Risk Object Type	Risk Score	Threat Objects
tried_accounts	user	54	src

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`
Integration	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`

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: 10