Detection: Detect DNS Query to Decommissioned S3 Bucket

EXPERIMENTAL DETECTION

This detection status is set to experimental. The Splunk Threat Research team has not yet fully tested, simulated, or built comprehensive datasets for this detection. As such, this analytic is not officially supported. If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2025-02-12 ID: 2f1c5fd1-4b8a-4f5d-a0e9-7d6a8e2f5e1e Author: Jose Hernandez, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This detection identifies DNS queries to domains that match previously decommissioned S3 buckets. This activity is significant because attackers may attempt to recreate deleted S3 buckets that were previously public to hijack them for malicious purposes. If successful, this could allow attackers to host malicious content or exfiltrate data through compromised bucket names that may still be referenced by legitimate applications.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Network_Resolution where DNS.message_type=QUERY by DNS.query DNS.src 
3| `drop_dm_object_name("DNS")` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| eval bucket_domain = lower(query) 
7| lookup decommissioned_buckets bucketName as bucket_domain OUTPUT bucketName as match 
8| where isnotnull(match) 
9| `detect_dns_query_to_decommissioned_s3_bucket_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 22	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
detect_dns_query_to_decommissioned_s3_bucket_filter	`search *`

detect_dns_query_to_decommissioned_s3_bucket_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
T1485	Data Destruction	Impact

Actions on Objectives

DE.AE

CIS 13

LAPSUS$

Lazarus Group

Sandworm Team

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

To successfully implement this detection, you need to be ingesting DNS query logs and have them mapped to the Network_Resolution data model. Additionally, ensure that the baseline search "Baseline Of Open S3 Bucket Decommissioning" is running and populating the decommissioned_buckets KVstore lookup.

Known False Positives

Some applications or scripts may continue to reference old S3 bucket names after they have been decommissioned. These should be investigated and updated to prevent potential security risks.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A DNS query to decommissioned S3 bucket $query$ was detected from host $src$

Risk Object	Risk Object Type	Risk Score	Threat Objects
src	system	30	query

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	Not Applicable	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`cloudtrail`	`aws:cloudtrail`
Integration	✅ Passing	Dataset	`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: 1