Detection: ASL AWS Network Access Control List Deleted

Updated Date: 2025-01-09 ID: e010ddf5-e9a5-44e5-bdd6-0c919ba8fc8b Author: 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`amazon_security_lake` api.operation=DeleteNetworkAclEntry status=Success 
 2| spath input=api.request.data path=egress output=egress 
 3| spath input=api.request.data path=networkAclId output=networkAclId 
 4| search egress=false 
 5| fillnull 
 6| stats count min(_time) as firstTime max(_time) as lastTime by api.operation actor.user.uid actor.user.account.uid http_request.user_agent src_endpoint.ip cloud.region networkAclId 
 7| rename actor.user.uid as user, src_endpoint.ip as src_ip, cloud.region as region, http_request.user_agent as user_agent, actor.user.account_uid as aws_account_id 
 8| `security_content_ctime(firstTime)`
 9| `security_content_ctime(lastTime)` 
10| `asl_aws_network_access_control_list_deleted_filter`

Data Source

Name	Platform	Sourcetype	Source
ASL AWS CloudTrail	AWS	`'aws:asl'`	`'aws_asl'`

Macros Used

Name	Value
amazon_security_lake	`sourcetype=aws:asl`
asl_aws_network_access_control_list_deleted_filter	`search *`

asl_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

Exploitation

DE.AE

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

The detection is based on Amazon Security Lake events from Amazon Web Services (AWS), which is a centralized data lake that provides security-related data from AWS services. To use this detection, you must ingest CloudTrail logs from Amazon Security Lake into Splunk. To run this search, ensure that you ingest events using the latest version of Splunk Add-on for Amazon Web Services (https://splunkbase.splunk.com/app/1876) or the Federated Analytics App.

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:

User $user$ from $src_ip$ has sucessfully deleted network ACLs entry.

Risk Object	Risk Object Type	Risk Score	Threat Objects
user	user	5	src_ip

Detection Testing

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

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: 1