CVE-2025-20298: Splunk Universal Forwarder Escalation

CVE-2025-20298 Overview

CVE-2025-20298 is an insecure permissions vulnerability affecting Splunk Universal Forwarder for Windows. During a new installation or upgrade to affected versions, incorrect permissions are assigned to the Universal Forwarder installation directory (by default, C:\Program Files\SplunkUniversalForwarder). This misconfiguration allows non-administrator users on the machine to access the directory and all its contents, potentially exposing sensitive configuration data, credentials, and enabling local privilege escalation.

Critical Impact

Non-administrator users can access the Splunk Universal Forwarder installation directory, potentially leading to credential theft, configuration tampering, and local privilege escalation on Windows systems.

Affected Products

• Splunk Universal Forwarder for Windows versions below 9.4.2
• Splunk Universal Forwarder for Windows versions below 9.3.4
• Splunk Universal Forwarder for Windows versions below 9.2.6
• Splunk Universal Forwarder for Windows versions below 9.1.9

Discovery Timeline

• 2025-06-02 - CVE-2025-20298 published to NVD
• 2025-08-04 - Last updated in NVD database

Technical Details for CVE-2025-20298

Vulnerability Analysis

This vulnerability is classified under CWE-732 (Incorrect Permission Assignment for Critical Resource). The flaw occurs during the installation or upgrade process of Splunk Universal Forwarder on Windows systems, where the installer fails to properly restrict access permissions on the installation directory.

The Splunk Universal Forwarder is a lightweight agent used to collect and forward log data to Splunk indexers. It typically contains sensitive configuration files including authentication credentials, SSL certificates, and connection parameters. When permissions are incorrectly assigned, any local user—regardless of their privilege level—can read, and potentially modify, these critical files.

This vulnerability requires local access to the affected system and user interaction during installation or upgrade, but once exploited, it can lead to significant security impacts including complete compromise of forwarder credentials and the ability to manipulate log collection.

Root Cause

The root cause is improper permission assignment during the Windows installation process. The installer fails to apply restrictive ACLs (Access Control Lists) to the C:\Program Files\SplunkUniversalForwarder directory and its subdirectories. Instead of limiting access to administrators and the SYSTEM account, the directory is left accessible to standard users, violating the principle of least privilege.

Attack Vector

The attack vector is network-based with local access requirements. An attacker with low-privilege access to a Windows system running an affected version of Splunk Universal Forwarder can exploit this vulnerability by:

1. Navigating to the Universal Forwarder installation directory
2. Accessing configuration files containing sensitive data such as inputs.conf, outputs.conf, and certificate files
3. Extracting credentials or SSL certificates for lateral movement
4. Modifying configuration files to redirect log data or inject malicious configurations

The vulnerability exposes sensitive configuration files that may contain authentication tokens, passwords, and SSL private keys used for secure communication with Splunk indexers.

Detection Methods for CVE-2025-20298

Indicators of Compromise

• Unexpected access to C:\Program Files\SplunkUniversalForwarder by non-administrator accounts
• Modifications to Splunk Universal Forwarder configuration files outside of authorized change windows
• Non-privileged users reading sensitive files such as server.conf, outputs.conf, or certificate files
• Unusual authentication attempts to Splunk infrastructure using forwarder credentials

Detection Strategies

• Audit file system access events for the SplunkUniversalForwarder directory using Windows Security Event logs (Event IDs 4663, 4656)
• Monitor for changes to Splunk configuration files using File Integrity Monitoring (FIM) solutions
• Implement SentinelOne's behavioral AI to detect anomalous access patterns to protected application directories
• Review Windows ACLs on the installation directory using PowerShell's Get-Acl cmdlet to identify overly permissive configurations

Monitoring Recommendations

• Enable Windows Object Access auditing for the Splunk Universal Forwarder installation directory
• Configure SentinelOne to alert on unauthorized file access to Splunk directories by non-system accounts
• Implement centralized logging to capture and correlate access attempts across affected endpoints
• Regularly scan systems for versions affected by this vulnerability using vulnerability management tools

How to Mitigate CVE-2025-20298

Immediate Actions Required

• Upgrade Splunk Universal Forwarder for Windows to version 9.4.2, 9.3.4, 9.2.6, or 9.1.9 or later depending on your version branch
• Manually verify and correct directory permissions on affected installations
• Rotate any credentials that may have been exposed, including Splunk authentication tokens and SSL certificates
• Audit systems for signs of unauthorized access to the Forwarder installation directory

Patch Information

Splunk has released patched versions addressing this vulnerability. Organizations should upgrade to the following minimum versions:

• Version 9.4.x: Upgrade to 9.4.2 or later
• Version 9.3.x: Upgrade to 9.3.4 or later
• Version 9.2.x: Upgrade to 9.2.6 or later
• Version 9.1.x: Upgrade to 9.1.9 or later

For detailed patch information, refer to the Splunk Security Advisory SVD-2025-0602.

Workarounds

• Manually set restrictive ACLs on the C:\Program Files\SplunkUniversalForwarder directory to limit access to Administrators and SYSTEM only
• Remove inherited permissions and apply explicit deny rules for non-privileged users
• Consider using Group Policy to enforce directory permissions across affected systems
• Implement application whitelisting to control which processes can access the Forwarder directory

# PowerShell script to correct permissions on Splunk Universal Forwarder directory
$splunkPath = "C:\Program Files\SplunkUniversalForwarder"
$acl = Get-Acl $splunkPath

# Remove inheritance and convert inherited permissions
$acl.SetAccessRuleProtection($true, $false)

# Define access rules for Administrators and SYSTEM only
$adminRule = New-Object System.Security.AccessControl.FileSystemAccessRule("BUILTIN\Administrators", "FullControl", "ContainerInherit,ObjectInherit", "None", "Allow")
$systemRule = New-Object System.Security.AccessControl.FileSystemAccessRule("NT AUTHORITY\SYSTEM", "FullControl", "ContainerInherit,ObjectInherit", "None", "Allow")

# Apply new permissions
$acl.SetAccessRule($adminRule)
$acl.SetAccessRule($systemRule)
Set-Acl -Path $splunkPath -AclObject $acl

Write-Host "Permissions corrected for $splunkPath"