Privilege Escalation Risk: Splunk Universal Forwarder on Windows

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A high-severity vulnerability has been discovered in Splunk Universal Forwarder (UF) for Windows, exposing enterprise systems to serious risk. Tracked as CVE-2025-20298, the flaw allows non-administrator users to gain unauthorized access to the application's installation directory and its contents.

With a CVSS v3.1 score of 8.0, this vulnerability violates fundamental security principles such as least privilege and may lead to log tampering, data exposure, and service disruption.



Overview of the Issue

During new installations or upgrades of Splunk Universal Forwarder on Windows, some affected versions assign overly permissive access controls to the installation directory:

C:\Program Files\SplunkUniversalForwarder

This misconfiguration allows standard (non-admin) users to read and potentially modify the contents of the directory, including configuration files, log data, and binary executables.

The issue is categorized under CWE-732: Incorrect Permission Assignment for Critical Resource, indicating a failure to properly restrict access to sensitive components.

Security Impact

Splunk Universal Forwarder is widely used to collect and forward log data from endpoints to centralized Splunk servers. Allowing non-privileged users access to this directory introduces several risks:

  • Unauthorized access to sensitive log data or configuration files

  • Potential tampering with forwarding configurations or scripts

  • Interruption or redirection of critical log flows

  • Violations of auditing, monitoring, or compliance requirements

Affected Versions

This vulnerability affects the following versions of Splunk Universal Forwarder for Windows:

  • 9.4.x: Versions earlier than 9.4.2

  • 9.3.x: Versions earlier than 9.3.4

  • 9.2.x: Versions earlier than 9.2.6

  • 9.1.x: Versions earlier than 9.1.9

Organizations running any of these versions are potentially vulnerable.

Exploitation Requirements

To exploit this issue, an attacker would need:

  • Local access to a Windows system running Splunk UF

  • A non-administrator user account

  • A vulnerable version of Splunk UF installed or recently upgraded

  • No permission fix or patch applied

Although user interaction is required, the attack complexity is low and the potential impact is high.

Remediation Options

Recommended: Upgrade to Patched Versions

Splunk has released updates that correct the permission assignment issue. Upgrade immediately to one of the following versions (or newer):

  • 9.4.2

  • 9.3.4

  • 9.2.6

  • 9.1.9

Upgrading is the most reliable and long-term solution.

Temporary Workaround: Fix Permissions Manually

If upgrading is not immediately possible, apply the following mitigation using an administrator-level Command Prompt or PowerShell window:

icacls "C:\Program Files\SplunkUniversalForwarder" /remove:g *BU /T /C

This command removes group permissions for the Built-in Users group from the UF directory and all subfolders:

  • /remove:g *BU removes permissions granted to standard users

  • /T applies the fix recursively

  • /C continues execution even if some files cause errors

This fix should be applied immediately after:

  • Installing a vulnerable version

  • Upgrading to a vulnerable version

  • Reinstalling Splunk Universal Forwarder on a Windows system

Organizations using Splunk Universal Forwarder in Windows environments should assess their deployments immediately. Given the sensitivity of log data and configuration files, any unauthorized access can lead to serious consequences. Prioritize upgrading to secure versions or apply the manual fix without delay.

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