Detection: Splunk DoS Using Malformed SAML Request

Updated Date: 2024-05-29 ID: 8e8a86d5-f323-4567-95be-8e817e2baee6 Author: Rod Soto Type: Hunting Product: Splunk Enterprise Security

Description

The following analytic detects a denial of service (DoS) attempt using a malformed SAML request targeting the /saml/acs REST endpoint in Splunk Enterprise versions lower than 9.0.6 and 8.2.12. It leverages splunkd logs, specifically looking for error messages containing "xpointer" in the expr field. This activity is significant because it can cause the Splunk daemon to crash or hang, disrupting service availability. If confirmed malicious, this attack could lead to prolonged downtime, impacting the organization's ability to monitor and respond to security events.

1`splunkd` event_message=*error* expr=*xpointer* 
2| stats count min(_time) as firstTime max(_time) as lastTime by component expr splunk_server event_message 
3| `security_content_ctime(firstTime)`
4| `security_content_ctime(lastTime)` 
5| `splunk_dos_using_malformed_saml_request_filter`

Data Source

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

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
splunk_dos_using_malformed_saml_request_filter search *
splunk_dos_using_malformed_saml_request_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
T1498 Network Denial of Service Impact
KillChainPhase.ACTIONS_ON_OBJECTIVES
NistCategory.DE_AE
Cis18Value.CIS_10
APT28

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

To run this search, you must have access to the _internal index.

Known False Positives

This search will show false positives. The analyst must look for errors and a pointer indicating a malicious file.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Possible DoS attack against Splunk Server $splunk_server$ 15 50 30
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

Detection Testing

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

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