Detection: Detect GCP Storage access from a new IP

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: 2024-10-17 ID: ccc3246a-daa1-11ea-87d0-0242ac130022 Author: Shannon Davis, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies access to GCP Storage buckets from new or previously unseen remote IP addresses. It leverages GCP Storage bucket-access logs ingested via Cloud Pub/Sub and compares current access events against a lookup table of previously seen IP addresses. This activity is significant as it may indicate unauthorized access or potential reconnaissance by an attacker. If confirmed malicious, this could lead to data exfiltration, unauthorized data manipulation, or further compromise of the GCP environment.

Search

 1`google_gcp_pubsub_message` 
 2| multikv 
 3| rename sc_status_ as status 
 4| rename cs_object_ as bucket_name 
 5| rename c_ip_ as remote_ip 
 6| rename cs_uri_ as request_uri 
 7| rename cs_method_ as operation 
 8| search status="\"200\"" 
 9| stats earliest(_time) as firstTime latest(_time) as lastTime by bucket_name remote_ip operation request_uri 
10| table firstTime, lastTime, bucket_name, remote_ip, operation, request_uri 
11| inputlookup append=t previously_seen_gcp_storage_access_from_remote_ip 
12| stats min(firstTime) as firstTime, max(lastTime) as lastTime by bucket_name remote_ip operation request_uri 
13| outputlookup previously_seen_gcp_storage_access_from_remote_ip 
14| eval newIP=if(firstTime >= relative_time(now(),"-70m@m"), 1, 0) 
15| where newIP=1 
16| eval first_time=strftime(firstTime,"%m/%d/%y %H:%M:%S") 
17| eval last_time=strftime(lastTime,"%m/%d/%y %H:%M:%S") 
18| table  first_time last_time bucket_name remote_ip operation request_uri 
19| `detect_gcp_storage_access_from_a_new_ip_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name	Value
google_gcp_pubsub_message	`sourcetype="google:gcp:pubsub:message"`
detect_gcp_storage_access_from_a_new_ip_filter	`search *`

detect_gcp_storage_access_from_a_new_ip_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
T1530	Data from Cloud Storage	Collection

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_13

Fox Kitten

Scattered Spider

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

This search relies on the Splunk Add-on for Google Cloud Platform, setting up a Cloud Pub/Sub input, along with the relevant GCP PubSub topics and logging sink to capture GCP Storage Bucket events (https://cloud.google.com/logging/docs/routing/overview). In order to capture public GCP Storage Bucket access logs, you must also enable storage bucket logging to your PubSub Topic as per https://cloud.google.com/storage/docs/access-logs. These logs are deposited into the nominated Storage Bucket on an hourly basis and typically show up by 15 minutes past the hour. It is recommended to configure any saved searches or correlation searches in Enterprise Security to run on an hourly basis at 30 minutes past the hour (cron definition of 30 * * * *). A lookup table (previously_seen_gcp_storage_access_from_remote_ip.csv) stores the previously seen access requests, and is used by this search to determine any newly seen IP addresses accessing the Storage Buckets.

Known False Positives

GCP Storage buckets can be accessed from any IP (if the ACLs are open to allow it), as long as it can make a successful connection. This will be a false postive, since the search is looking for a new IP within the past two hours.

Associated Analytic Story

Suspicious GCP Storage Activities

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
tbd	25	50	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	Not Applicable	N/A	N/A	N/A
Unit	❌ Failing	N/A	`N/A`	`N/A`
Integration	❌ Failing	N/A	`N/A`	`N/A`

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