Detection: AWS Network Access Control List Deleted

Updated Date: 2024-05-15 ID: ada0f478-84a8-4641-a3f1-d82362d6fd75 Author: Bhavin Patel, Patrick Bareiss, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects the deletion of AWS Network Access Control Lists (ACLs). It leverages AWS CloudTrail logs to identify events where a user deletes a network ACL entry. This activity is significant because deleting a network ACL can remove critical access restrictions, potentially allowing unauthorized access to cloud instances. If confirmed malicious, this action could enable attackers to bypass network security controls, leading to unauthorized access, data exfiltration, or further compromise of the cloud environment.

Search

1`cloudtrail` eventName=DeleteNetworkAclEntry requestParameters.egress=false 
2| fillnull 
3| stats count min(_time) as firstTime max(_time) as lastTime by user_arn userIdentity.principalId eventName requestParameters.egress src userAgent 
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)` 
6| `aws_network_access_control_list_deleted_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
AWS CloudTrail DeleteNetworkAclEntry	AWS	`'aws:cloudtrail'`	`'aws_cloudtrail'`	N/A

Macros Used

Name	Value
cloudtrail	`sourcetype=aws:cloudtrail`
aws_network_access_control_list_deleted_filter	`search *`

aws_network_access_control_list_deleted_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1562.007	Disable or Modify Cloud Firewall	Defense Evasion
T1562	Impair Defenses	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_13

Magic Hound

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

You must install the AWS App for Splunk (version 5.1.0 or later) and Splunk Add-on for AWS (version 4.4.0 or later), then configure your AWS CloudTrail inputs.

Known False Positives

It's possible that a user has legitimately deleted a network ACL.

Associated Analytic Story

AWS Network ACL Activity

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
User $user_arn$ from $src$ has sucessfully deleted network ACLs entry (eventName= $eventName$), such that the instance is accessible from anywhere	5	10	50

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

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`
Integration	✅ Passing	Dataset	`aws_cloudtrail`	`aws:cloudtrail`

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: GitHub | Version: 3