Try in Splunk Security Cloud

Description

The following analytic identifies the creation of open/public S3 buckets in AWS. It detects this activity by analyzing AWS CloudTrail events for PutBucketAcl actions where the access control list (ACL) grants permissions to all users or authenticated users. This activity is significant because open S3 buckets can expose sensitive data to unauthorized access, leading to data breaches. If confirmed malicious, an attacker could read, write, or fully control the contents of the bucket, potentially leading to data exfiltration or tampering.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-05-19
  • Author: Bhavin Patel, Patrick Bareiss, Splunk
  • ID: 2a9b80d3-6340-4345-b5ad-290bf3d0dac4

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1530 Data from Cloud Storage Collection
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


1
2
3
4
5
6
7
8
9
10
11
12
13
14



`cloudtrail` eventSource=s3.amazonaws.com eventName=PutBucketAcl 
| rex field=_raw "(?<json_field>{.+})" 
| spath input=json_field output=grantees path=requestParameters.AccessControlPolicy.AccessControlList.Grant{} 
| search grantees=* 
| mvexpand grantees 
| spath input=grantees output=uri path=Grantee.URI 
| spath input=grantees output=permission path=Permission 
| search uri IN ("http://acs.amazonaws.com/groups/global/AllUsers","http://acs.amazonaws.com/groups/global/AuthenticatedUsers") 
| search permission IN ("READ","READ_ACP","WRITE","WRITE_ACP","FULL_CONTROL") 
| rename requestParameters.bucketName AS bucketName 
| stats count min(_time) as firstTime max(_time) as lastTime by user_arn userIdentity.principalId userAgent uri permission bucketName 
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)` 
| `detect_new_open_s3_buckets_filter`

Macros

The SPL above uses the following Macros:

:information_source: detect_new_open_s3_buckets_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
  • eventSource
  • eventName
  • requestParameters.bucketName
  • user_arn
  • userIdentity.principalId
  • userAgent
  • uri
  • permission

How To Implement

You must install the AWS App for Splunk.

Known False Positives

While this search has no known false positives, it is possible that an AWS admin has legitimately created a public bucket for a specific purpose. That said, AWS strongly advises against granting full control to the "All Users" group.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
48.0 60 80 User $user_arn$ has created an open/public bucket $bucketName$ with the following permissions $permission$

: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: 4