Splunk Local Privilege Escalation

Vulnerability Description

Splunk can be configured to run as a non-root user. However, that user owns the configuration file that specifies the user to run as, so it can trivially gain root privileges.

Technical Description

Splunk runs multiple daemons and network listeners as root by default. It can be configured to drop privileges to a specified non-root user at startup such as user splunk, via the SPLUNK_OS_USER variable in the splunk-launch.conf file in $SPLUNK_HOME/etc/ (such as /opt/splunk/etc/splunk-launch.conf).

However, the instructions for enabling such a setup call for chown’ing the entire $SPLUNK_HOME directory to that same non-root user. For instance:

http://docs.splunk.com/Documentation/Splunk/6.6.2/Installation/RunSplunkasadifferentornon-rootuser

“4. Run the chown command to change the ownership of the splunk directory and everything under it to the user that you want to run the software.

     chown -R splunk:splunk $SPLUNK_HOME"

Therefore, if an attacker gains control of the splunk account, they can modify $SPLUNK_HOME/etc/splunk-launch.conf to remove/unset SPLUNK_OS_USER so that the software will retain root privileges, and place backdoors under $SPLUNK_HOME/bin/, etc. that will take malicious actions as user root the next time Splunk is restarted.

Mitigation and Remediation Recommendation

The vendor has published a mitigation for this vulnerability at: https://www.splunk.com/view/SP-CAAAP3M

Credit

This vulnerability was discovered by Hank Leininger of KoreLogic, Inc.

Proof of Concept

See 3. Technical Description.

The contents of this advisory are copyright(c) 2017 KoreLogic, Inc. and are licensed under a Creative Commons Attribution Share-Alike 4.0 (United States) License: http://creativecommons.org/licenses/by-sa/4.0/

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