Detection: Detect Web Access 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: 3a1d8f62-5b9c-4e7d-b8f3-9d6a8e2f5e1f Author: Jose Hernandez, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This detection identifies web requests to domains that match previously decommissioned S3 buckets through web proxy logs. This activity is significant because attackers may attempt to access or 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.

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime values(Web.http_method) as http_method values(Web.http_user_agent) as http_user_agent values(Web.url) as url values(Web.user) as user from datamodel=Web where Web.url_domain!="" by Web.src Web.url_domain 
3| `drop_dm_object_name("Web")` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| eval bucket_domain = lower(url_domain) 
7| lookup decommissioned_buckets bucketName as bucket_domain OUTPUT bucketName as match 
8| where isnotnull(match) 
9| `detect_web_access_to_decommissioned_s3_bucket_filter`

Data Source

Name Platform Sourcetype Source
AWS Cloudfront AWS icon AWS 'aws:cloudfront:accesslogs' 'aws'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
detect_web_access_to_decommissioned_s3_bucket_filter search *
detect_web_access_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

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 web proxy logs and have them mapped to the Web 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 web pages may continue to reference old S3 bucket URLs 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 web request to decommissioned S3 bucket domain $url_domain$ was detected from host $src$ by user $user$

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

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