Detection: Splunk DoS via Malformed S2S Request

Date: 2024-05-27 ID: fc246e56-953b-40c1-8634-868f9e474cbd Author: Lou Stella, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies attempts to exploit a Denial of Service (DoS) vulnerability in the Splunk-to-Splunk (S2S) protocol by detecting malformed S2S requests. It leverages splunkd logs, specifically looking for "ERROR" level logs from the "TcpInputProc" component with the thread name "FwdDataReceiverThread" and the message "Invalid _meta atom." This activity is significant as it targets a known vulnerability that could disrupt Splunk services. If confirmed malicious, this could lead to service outages, impacting the availability and reliability of Splunk for monitoring and analysis.

1`splunkd` log_level="ERROR" component="TcpInputProc" thread_name="FwdDataReceiverThread" "Invalid _meta atom" 
2| table host, src 
3| `splunk_dos_via_malformed_s2s_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
splunkd index=_internal sourcetype=splunkd
splunk_dos_via_malformed_s2s_request_filter search *
splunk_dos_via_malformed_s2s_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_CM
Cis18Value.CIS_10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Enabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Risk Based Alerting True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

This detection does not require you to ingest any new data. The detection does require the ability to search the _internal index. This detection will only find attempted exploitation on versions of Splunk already patched for CVE-2021-3422.

Known False Positives

None.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
An attempt to exploit CVE-2021-3422 was detected from $src$ against $host$ 50 50 100
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

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset /opt/splunk/var/log/splunk/splunkd.log splunkd
Integration ✅ Passing Dataset /opt/splunk/var/log/splunk/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: 3