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Description

This search looks for AssumeRole events where an IAM role in a different account is requested for the first time.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Authentication
  • Last Updated: 2020-05-28
  • Author: Rico Valdez, Splunk
  • ID: 21193641-cb96-4a2c-a707-d9b9a7f7792b

Annotations

ATT&CK
Kill Chain Phase
  • Actions on Objectives
NIST
  • PR.AC
  • PR.DS
  • DE.AE
CIS20
  • CIS 16
CVE
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| tstats min(_time) as firstTime max(_time) as lastTime from datamodel=Authentication where Authentication.signature=AssumeRole by Authentication.vendor_account Authentication.user Authentication.src Authentication.user_role 
| `drop_dm_object_name(Authentication)` 
| rex field=user_role "arn:aws:sts:*:(?<dest_account>.*):" 
| where vendor_account != dest_account 
| rename vendor_account as requestingAccountId dest_account as requestedAccountId 
| lookup previously_seen_aws_cross_account_activity requestingAccountId, requestedAccountId, OUTPUTNEW firstTime 
| eval status = if(firstTime > relative_time(now(), "-24h@h"),"New Cross Account Activity","Previously Seen") 
|  where status = "New Cross Account Activity" 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)`
| `aws_cross_account_activity_from_previously_unseen_account_filter`

Macros

The SPL above uses the following Macros:

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

Lookups

The SPL above uses the following Lookups:

Required field

  • _time
  • Authentication.signature
  • Authentication.vendor_account
  • Authentication.user
  • Authentication.user_role
  • Authentication.src

How To Implement

You must be ingesting your cloud infrastructure logs from your cloud provider. You should run the baseline search Previously Seen AWS Cross Account Activity - Initial to build the initial table of source IP address, geographic locations, and times. You must also enable the second baseline search Previously Seen AWS Cross Account Activity - Update to keep this table up to date and to age out old data. You can also provide additional filtering for this search by customizing the aws_cross_account_activity_from_previously_unseen_account_filter macro.

Known False Positives

Using multiple AWS accounts and roles is perfectly valid behavior. It’s suspicious when an account requests privileges of an account it hasn’t before. You should validate with the account owner that this is a legitimate request.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
15.0 30 50 AWS account $requestingAccountId$ is trying to access resource from some other account $requestedAccountId$, for the first time.

: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: 1