Detection: Splunk RBAC Bypass On Indexing Preview REST Endpoint

Updated Date: 2024-10-17 ID: bbe26f95-1655-471d-8abd-3d32fafa86f8 Author: Rod Soto Type: Hunting Product: Splunk Enterprise Security

Description

The following analytic identifies unauthorized attempts to use the /services/indexing/preview REST endpoint in Splunk. It detects POST requests to this endpoint by monitoring the _internal index for specific URI patterns. This activity is significant because it indicates a potential RBAC (Role-Based Access Control) bypass, allowing unauthorized users to overwrite search results if they know the search ID (SID) of an existing job. If confirmed malicious, this could lead to data manipulation, unauthorized access to sensitive information, and compromised integrity of search results.

Search

1`splunkda` method="POST" uri="*/services/indexing/preview*" 
2| table host clientip status useragent user uri_path 
3| `splunk_rbac_bypass_on_indexing_preview_rest_endpoint_filter`

Data Source

Name	Platform	Sourcetype	Source
Splunk	Splunk	`'splunkd_ui_access'`	`'splunkd_ui_access.log'`

Macros Used

Name	Value
splunkda	`index=_internal sourcetype=splunkd_access`
splunk_rbac_bypass_on_indexing_preview_rest_endpoint_filter	`search *`

splunk_rbac_bypass_on_indexing_preview_rest_endpoint_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
T1134	Access Token Manipulation	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_10

Blue Mockingbird

FIN6

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	False

This configuration file applies to all detections of type hunting.

Implementation

This search does not require additional data ingestion. It requires the ability to search _internal index.

Known False Positives

This is a hunting search which provides verbose results against this endpoint. Operator must consider things such as IP address, useragent and user(specially low privelege) and host to investigate possible attack.

Associated Analytic Story

Splunk Vulnerabilities

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Review $clientip$ access to indexing preview endpoint from low privilege user	15	30	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.

References

https://advisory.splunk.com/

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`splunkd_access.log`	`splunkd_access`
Integration	✅ Passing	Dataset	`splunkd_access.log`	`splunkd_access`

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