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Description

The following detection identifies excessive AccessDenied events within an hour timeframe. It is possible that an access key to AWS may have been stolen and is being misused to perform discovery events. In these instances, the access is not available with the key stolen therefore these events will be generated.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud, Splunk Security Analytics for AWS
  • Datamodel:
  • Last Updated: 2021-11-12
  • Author: Michael Haag, Splunk
  • ID: 3e1f1568-9633-11eb-a69c-acde48001122

ATT&CK

ID Technique Tactic
T1580 Cloud Infrastructure Discovery Discovery
`cloudtrail` (errorCode = "AccessDenied") user_type=IAMUser (userAgent!=*.amazonaws.com) 
| bucket _time span=1h 
| stats count as failures min(_time) as firstTime max(_time) as lastTime, dc(eventName) as methods, dc(eventSource) as sources by src_ip, userIdentity.arn, _time 
| where failures >= 5 and methods >= 1 and sources >= 1 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `aws_iam_accessdenied_discovery_events_filter`

Associated Analytic Story

How To Implement

The Splunk AWS Add-on and Splunk App for AWS is required to utilize this data. The search requires AWS Cloudtrail logs.

Required field

  • _time
  • eventName
  • eventSource
  • userAgent
  • errorCode
  • userIdentity.type

Kill Chain Phase

  • Reconnaissance

Known False Positives

It is possible to start this detection will need to be tuned by source IP or user. In addition, change the count values to an upper threshold to restrict false positives.

RBA

Risk Score Impact Confidence Message
10.0 20 50 User $userIdentity.arn$ is seen to perform excessive number of discovery related api calls- $failures$, within an hour where the access was denied.

Reference

Test Dataset

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 | version: 2