Detection: Splunk DOS via printf search function

Updated Date: 2024-05-25 ID: 78b48d08-075c-4eac-bd07-e364c3780867 Author: Rod Soto, Eric McGinnis, Splunk Type: Hunting Product: Splunk Enterprise Security

Description

The following analytic identifies the use of the printf SPL function in Splunk searches, which can be exploited for a denial of service (DoS) attack. It detects this activity by querying the audit_searches data source for specific patterns involving makeresults, eval, fieldformat, and printf functions, excluding searches by the splunk_system_user. This activity is significant because it targets a known vulnerability in Splunk Enterprise versions lower than 8.1.14, 8.2.12, 9.0.6, and 9.1.1, potentially disrupting the availability of the Splunk instance. If confirmed malicious, this could lead to service outages and impact the monitoring and logging capabilities of the organization.

Search

1`audit_searches` "*makeresults * eval * fieldformat *printf*" user!="splunk_system_user" search!="*audit_searches*" 
2| stats count by user splunk_server host search 
3| convert ctime(*time) 
4|`splunk_dos_via_printf_search_function_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Splunk	Splunk	`'splunkd_ui_access'`	`'splunkd_ui_access.log'`	N/A

Macros Used

Name	Value
audit_searches	`index=_audit sourcetype=audittrail action=search`
splunk_dos_via_printf_search_function_filter	`search *`

splunk_dos_via_printf_search_function_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
T1499.004	Application or System Exploitation	Impact

KillChainPhase.ACTIONS_ON_OBJECTIVES

NistCategory.DE_AE

Cis18Value.CIS_10

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 requires the ability to search internal indexes.

Known False Positives

This search may produces false positives, analyst most focuse in the use of printf conversion function of eval to craft an expression that splunkd cannot interpret correctly causing it to crash.

Associated Analytic Story

Splunk Vulnerabilities

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Possible denial of service attack against $host$	100	100	100

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	`audittrail`	`audittrail`
Integration	✅ Passing	Dataset	`audittrail`	`audittrail`

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: 2