AWS EC2 Snapshot Shared Externally

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Description

The following analytic utilizes AWS CloudTrail events to identify when an EC2 snapshot permissions are modified to be shared with a different AWS account. This method is used by adversaries to exfiltrate the EC2 snapshot.

• Type: TTP

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

• Last Updated: 2023-03-20
• Author: Bhavin Patel, Splunk
• ID: 2a9b80d3-6340-4345-b5ad-290bf3d222c4

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1537	Transfer Data to Cloud Account	Exfiltration

Kill Chain Phase

• Actions On Objectives

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

`cloudtrail` eventName=ModifySnapshotAttribute 
| rename requestParameters.createVolumePermission.add.items{}.userId as requested_account_id 
| search requested_account_id != NULL 
| eval match=if(requested_account_id==aws_account_id,"Match","No Match") 
| table _time user_arn src_ip requestParameters.attributeType requested_account_id aws_account_id match vendor_region user_agent userIdentity.principalId 
| where match = "No Match" 
| `aws_ec2_snapshot_shared_externally_filter` 

Macros

The SPL above uses the following Macros:

• cloudtrail

aws_ec2_snapshot_shared_externally_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
• user_arn
• src_ip
• requestParameters.attributeType
• aws_account_id
• vendor_region
• user_agent
• userIdentity.principalId

How To Implement

You must install splunk AWS add on and Splunk App for AWS. This search works with AWS CloudTrail logs.

Known False Positives

It is possible that an AWS admin has legitimately shared a snapshot with others for a specific purpose.

Associated Analytic Story

• Suspicious Cloud Instance Activities
• Data Exfiltration

RBA

Risk Score	Impact	Confidence	Message
48.0	60	80	AWS EC2 snapshot from account $aws_account_id$ is shared with $requested_account_id$ by user $user_arn$ from $src_ip$

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

• https://labs.nettitude.com/blog/how-to-exfiltrate-aws-ec2-data/
• https://stratus-red-team.cloud/attack-techniques/AWS/aws.exfiltration.ec2-share-ebs-snapshot/
• https://hackingthe.cloud/aws/enumeration/loot_public_ebs_snapshots/

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: 3