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On March 24th, 2022, Splunk published a security advisory for a possible Denial of Service stemming from the lack of validation in a specific key-value field in the Splunk-to-Splunk (S2S) protocol. This detection will alert on attempted exploitation in patched versions of Splunk.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2022-03-24
  • Author: Lou Stella, Splunk
  • ID: fc246e56-953b-40c1-8634-868f9e474cbd




ID Technique Tactic
T1498 Network Denial of Service Impact
Kill Chain Phase
  • Actions On Objectives
  • DE.CM
  • CIS 10
ID Summary CVSS
CVE-2021-3422 The lack of validation of a key-value field in the Splunk-to-Splunk protocol results in a denial-of-service in Splunk Enterprise instances configured to index Universal Forwarder traffic. The vulnerability impacts Splunk Enterprise versions before 7.3.9, 8.0 versions before 8.0.9, and 8.1 versions before 8.1.3. It does not impact Universal Forwarders. When Splunk forwarding is secured using TLS or a Token, the attack requires compromising the certificate or token, or both. Implementation of either or both reduces the severity to Medium. 4.3
`splunkd` log_level="ERROR" component="TcpInputProc" thread_name="FwdDataReceiverThread" "Invalid _meta atom" 
| table host, src 
| `splunk_dos_via_malformed_s2s_request_filter`


The SPL above uses the following Macros:

:information_source: splunk_dos_via_malformed_s2s_request_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • host
  • src
  • log_level
  • component
  • thread_name

How To Implement

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


Associated Analytic Story


Risk Score Impact Confidence Message
50.0 50 100 An attempt to exploit CVE-2021-3422 was detected from $src$ against $host$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.


Test Dataset

Replay any dataset to Splunk Enterprise by using our tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 2