CVE-2017-18348 in Splunk
Summary
by MITRE
Splunk Enterprise 6.6.x, when configured to run as root but drop privileges to a specific non-root account, allows local users to gain privileges by leveraging access to that non-root account to modify $SPLUNK_HOME/etc/splunk-launch.conf and insert Trojan horse programs into $SPLUNK_HOME/bin, because the non-root setup instructions state that chown should be run across all of $SPLUNK_HOME to give non-root access.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 04/05/2020
This vulnerability exists in Splunk Enterprise version 6.6.x where the software is designed to run initially as the root user to perform necessary system-level operations but subsequently drops privileges to a specific non-root account for ongoing operations. The flaw arises from the privilege dropping mechanism and how file ownership permissions are handled during the setup process. When Splunk is configured to run as root initially, it performs operations that require elevated privileges, but then transitions to a non-root user account for routine operations. The vulnerability occurs because the setup instructions provided by Splunk explicitly recommend running chown commands across the entire $SPLUNK_HOME directory to grant the non-root user access to all files and directories. This approach creates a dangerous security boundary where a local user with access to the non-root account can manipulate the privilege escalation process by modifying the splunk-launch.conf file, which controls how Splunk handles privilege dropping.
The technical implementation of this vulnerability stems from the improper handling of file permissions and ownership during Splunk's initialization process. When the chown command is executed across the entire $SPLUNK_HOME directory, it grants the non-root user full write access to critical system files including the splunk-launch.conf configuration file. This configuration file is crucial because it determines how Splunk manages its privilege levels and can contain directives that influence the execution of programs within the Splunk environment. Attackers can exploit this by inserting malicious Trojan horse programs into the $SPLUNK_HOME/bin directory, which will then be executed with elevated privileges when Splunk runs. The vulnerability represents a classic privilege escalation flaw that can be categorized under CWE-276, which deals with incorrect permissions for critical resources, and also aligns with ATT&CK technique T1068 which covers privilege escalation through local exploitation of system vulnerabilities.
The operational impact of this vulnerability is significant as it allows local users to achieve privilege escalation from a non-root account to root privileges, effectively bypassing the intended security model of Splunk Enterprise. This escalation occurs because the malicious program inserted into the bin directory executes with the same privileges as the root user that initially started the Splunk service. Once the privilege escalation is achieved, attackers can perform actions such as modifying system files, installing backdoors, accessing sensitive data, and potentially compromising the entire system. The vulnerability is particularly dangerous because it leverages legitimate system configuration practices rather than exploiting unknown weaknesses, making it harder to detect through traditional security monitoring. Organizations using Splunk Enterprise 6.6.x are at risk of having their systems compromised if local users with access to the Splunk non-root account can modify system files, as this represents a fundamental breakdown in the privilege separation mechanism that is essential for maintaining system security.
The recommended mitigations for this vulnerability include several approaches that address the root cause of the privilege escalation issue. Organizations should avoid using the chown command that grants write permissions to the entire $SPLUNK_HOME directory structure when setting up Splunk with non-root accounts. Instead, they should implement more granular permission controls that only grant necessary access to specific files and directories. The most effective approach is to ensure that the splunk-launch.conf file and other critical configuration files are protected with immutable permissions that prevent modification by non-root users. Additionally, organizations should consider upgrading to Splunk Enterprise versions that have addressed this specific privilege escalation vulnerability through improved permission handling and privilege dropping mechanisms. Regular security audits should be conducted to verify that file ownership and permissions are properly configured, and monitoring should be implemented to detect any unauthorized modifications to critical Splunk configuration files. System administrators should also implement principle of least privilege practices, ensuring that Splunk is configured to run with the minimum necessary privileges and that any privilege escalation capabilities are carefully controlled and monitored.