Detection: Splunk DoS via Malformed S2S Request

REMOVED DETECTION

This detection has been removed from the Splunk Threat Research content library and is no longer maintained or supported.

Reason: Detection is deprecated as the associated CVEs have been patched in the latest Splunk release.

Removed in version: 5.6.0

If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2026-05-14 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.

Search

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
Splunk	Splunk	`'splunkd_ui_access'`	`'splunkd_ui_access.log'`

Macros Used

Name	Value
splunkd	`index=_internal sourcetype=splunkd`
splunk_dos_via_malformed_s2s_request_filter	``

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

CVE

CVE-2021-3422

Default Configuration

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

Setting	Value
Disabled	true
Cron Schedule	`N/A`
Earliest Time	`N/A`
Latest Time	`N/A`
Schedule Window	`N/A`
Creates Finding (Notable)	No
Creates Intermediate Finding (Risk Event)	No

TTP detections generate a Finding (Notable) and may generate Intermediate Findings (Risk Events) for associated entities.

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

Splunk Vulnerabilities

References

https://www.splunk.com/en_us/product-security/announcements/svd-2022-0301.html

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	Not Applicable	N/A	N/A	N/A
Unit	Not Applicable	N/A	`N/A`	`N/A`
Integration	Not Applicable	N/A	`N/A`	`N/A`

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: 7