:warning: THIS IS A EXPERIMENTAL DETECTION

This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

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Description

This search looks at GCP Storage bucket-access logs and detects new or previously unseen remote IP addresses that have successfully accessed a GCP Storage bucket.

  • Type: Anomaly

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2020-08-10
  • Author: Shannon Davis, Splunk
  • ID: ccc3246a-daa1-11ea-87d0-0242ac130022

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1530 Data from Cloud Storage Collection
Kill Chain Phase
  • Exploitation
NIST
  • DE.AE
CIS20
  • CIS 13
CVE 


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`google_gcp_pubsub_message` 
| multikv 
| rename sc_status_ as status 
| rename cs_object_ as bucket_name 
| rename c_ip_ as remote_ip 
| rename cs_uri_ as request_uri 
| rename cs_method_ as operation 
| search status="\"200\"" 
| stats earliest(_time) as firstTime latest(_time) as lastTime by bucket_name remote_ip operation request_uri 
| table firstTime, lastTime, bucket_name, remote_ip, operation, request_uri 
| inputlookup append=t previously_seen_gcp_storage_access_from_remote_ip 
| stats min(firstTime) as firstTime, max(lastTime) as lastTime by bucket_name remote_ip operation request_uri 
| outputlookup previously_seen_gcp_storage_access_from_remote_ip 
| eval newIP=if(firstTime >= relative_time(now(),"-70m@m"), 1, 0) 
| where newIP=1 
| eval first_time=strftime(firstTime,"%m/%d/%y %H:%M:%S") 
| eval last_time=strftime(lastTime,"%m/%d/%y %H:%M:%S") 
| table  first_time last_time bucket_name remote_ip operation request_uri 
| `detect_gcp_storage_access_from_a_new_ip_filter`

Macros

The SPL above uses the following Macros:

:information_source: detect_gcp_storage_access_from_a_new_ip_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Lookups

The SPL above uses the following Lookups:

Required fields

List of fields required to use this analytic.

  • _time
  • sc_status_
  • cs_object_
  • c_ip_
  • cs_uri_
  • cs_method_

How To Implement

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

RBA

Risk Score Impact Confidence Message
25.0 50 50 tbd

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

Reference

Test Dataset

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 | version: 1