CVE-2023-40596: Splunk Enterprise Privilege Escalation

CVE-2023-40596 Overview

CVE-2023-40596 is a privilege escalation vulnerability affecting Splunk Enterprise on Windows systems. The vulnerability exists because a dynamic link library (DLL) shipped with Splunk Enterprise references an insecure path for the OPENSSLDIR build definition. An attacker with local access can exploit this insecure path reference to install malicious code and achieve privilege escalation on the target Windows machine.

Critical Impact

Local attackers can leverage the insecure OPENSSLDIR path reference to plant malicious DLLs and escalate privileges, potentially gaining complete control over the affected Windows system running Splunk Enterprise.

Affected Products

• Splunk Enterprise versions earlier than 8.2.12
• Splunk Enterprise versions earlier than 9.0.6
• Splunk Enterprise version 9.1.0 (fixed in 9.1.1)

Discovery Timeline

• August 30, 2023 - CVE-2023-40596 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-40596

Vulnerability Analysis

This vulnerability falls under the categories of Improper Initialization (CWE-665) and Uncontrolled Search Path Element (CWE-427). The core issue stems from how OpenSSL was built for inclusion in Splunk Enterprise. During the build process, the OPENSSLDIR variable was set to an insecure path that an attacker with local access can write to. When Splunk Enterprise components attempt to load OpenSSL libraries, they follow this insecure path definition, allowing an attacker to place malicious code in that location.

The attack vector is local, requiring the attacker to already have some level of access to the Windows system running Splunk Enterprise. However, once exploited, the vulnerability allows for a scope change, meaning the attacker can break out of the vulnerable component's security context and impact resources beyond its security boundary. This can result in complete compromise of confidentiality, integrity, and availability of the system.

Root Cause

The root cause is an insecure build configuration where the OPENSSLDIR build definition in the OpenSSL libraries bundled with Splunk Enterprise points to a path that may be writable by low-privileged users. This is a classic uncontrolled search path element vulnerability combined with improper initialization of security-sensitive defaults during the software build process.

Attack Vector

The exploitation of this vulnerability requires the following conditions:

1. The attacker must have local access to the Windows machine running a vulnerable version of Splunk Enterprise
2. The attacker needs write access to the directory specified by the insecure OPENSSLDIR path
3. The attacker places a malicious DLL or configuration file in the vulnerable path
4. When Splunk Enterprise (or its OpenSSL components) loads, it references the attacker-controlled location
5. The malicious code executes with the privileges of the Splunk Enterprise service, resulting in privilege escalation

The exploitation mechanism leverages the trust that the OpenSSL library places in the configured OPENSSLDIR path to load configuration files or additional modules. By hijacking this path, attackers can inject malicious payloads that execute within the context of the Splunk service. For detailed technical information, refer to the Splunk Security Advisory SVD-2023-0805.

Detection Methods for CVE-2023-40596

Indicators of Compromise

• Unexpected files appearing in OpenSSL-related directories on the system, particularly in non-standard or world-writable paths
• Unusual DLL loading events associated with Splunk Enterprise processes
• New or modified files in directories that match the insecure OPENSSLDIR path pattern
• Anomalous process activity spawned from Splunk Enterprise services with elevated privileges

Detection Strategies

• Monitor file system changes in paths typically associated with OpenSSL configurations on Windows systems running Splunk
• Implement application allowlisting to detect unauthorized DLLs being loaded by Splunk processes
• Use endpoint detection and response (EDR) solutions like SentinelOne to identify DLL injection attempts and suspicious privilege escalation patterns
• Audit Splunk Enterprise service execution for abnormal child processes or network connections

Monitoring Recommendations

• Enable Windows Security Event logging for file creation and modification events in system directories
• Deploy SentinelOne agents configured to detect DLL sideloading and hijacking techniques
• Establish baseline behavior for Splunk Enterprise processes and alert on deviations
• Monitor for attempts to write to directories in the OpenSSL search path by non-administrative users

How to Mitigate CVE-2023-40596

Immediate Actions Required

• Upgrade Splunk Enterprise to version 8.2.12, 9.0.6, or 9.1.1 (or later) immediately
• Audit current Splunk Enterprise installations to identify vulnerable versions
• Restrict write permissions on directories that may be referenced by the insecure OPENSSLDIR path
• Review system logs for any signs of exploitation prior to patching

Patch Information

Splunk has released patched versions that address this vulnerability by correcting the OPENSSLDIR build definition to reference a secure, protected path. The following versions contain the fix:

• Splunk Enterprise 8.2.12 and later (for the 8.2.x branch)
• Splunk Enterprise 9.0.6 and later (for the 9.0.x branch)
• Splunk Enterprise 9.1.1 and later (for the 9.1.x branch)

For complete patch details and download links, refer to the Splunk Security Advisory SVD-2023-0805.

Workarounds

• If immediate patching is not possible, restrict file system permissions on potentially vulnerable paths to prevent unauthorized writes
• Implement application control policies to prevent unauthorized DLL loading by Splunk processes
• Consider running Splunk Enterprise with a dedicated service account that has minimal privileges beyond what is required for operation
• Use SentinelOne's behavioral AI to detect and block privilege escalation attempts targeting Splunk Enterprise

# Example: Identify Splunk Enterprise version on Windows
# Run from PowerShell to check installed version
Get-Content "C:\Program Files\Splunk\etc\splunk.version"

# Restrict permissions on potential vulnerable paths (example)
icacls "C:\path\to\openssldir" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" /grant:r "Administrators:(OI)(CI)F"