S2S TcpToken authentication bypass

Advisory ID: SVD-2022-0503

CVE ID: CVE-2021-31559

Published: 2022-05-03

Last Update: 2022-05-03

CVSSv3.1 Score: 7.5, High

CWE: CWE-288

Bug ID: SPL-203370


A crafted request bypasses S2S TCP Token authentication writing arbitrary events to an index in Splunk Enterprise Indexer 8.1 versions before 8.1.5 and 8.2 versions before 8.2.1. The vulnerability impacts Indexers configured to use TCPTokens. It does not impact Universal Forwarders.

See Enable a receiver for more information on configuring an indexer to listen for UF traffic. See Control forwarder access for more information on securing UF to Indexer traffic with TcpTokens.

When Splunk forwarding is secured using TLS, the attack requires compromising the certificate. As a partial mitigation and a security best practice, see Configure Splunk forwarding to use your own SSL certificates. Implementation reduces the severity to Medium.


Upgrade Splunk Enterprise Indexer 8.1 versions to 8.1.5 or later and 8.2.0 versions to 8.2.1 or later.

Product Status

ProductVersionComponentAffected VersionFix Version
Splunk Enterprise8.1-8.1.4 and earlier8.1.5
Splunk Enterprise8.2-

The vulnerability does not impact Splunk Cloud Platform instances.


Chris Samley at GE


2022-05-26: Added “Chris Samley at GE” to the Acknowledgments section.