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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

  • Last Updated: 2021-11-12
  • Author: Michael Haag, Splunk
  • ID: 3e1f1568-9633-11eb-a69c-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1580 Cloud Infrastructure Discovery Discovery
Kill Chain Phase
  • Reconnaissance
NIST
CIS20
CVE 


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`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`

Macros

The SPL above uses the following Macros:

:information_source: aws_iam_accessdenied_discovery_events_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

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

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.

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.

Associated Analytic Story

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.

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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