Splunk Universal Forwarder for Windows Flaw Grants Non-Admin Users Full Content Access

A critical security advisory (SVD-2025-0602) has been issued for Splunk Universal Forwarder for Windows, addressing a high-severity vulnerability (CVE-2025-20298) that exposes Windows systems to potential privilege escalation.

The flaw, rated 8.0 (High) on the CVSSv3.1 scale (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H), affects Universal Forwarder installations and upgrades below versions 9.4.2, 9.3.4, 9.2.6, and 9.1.9.

The vulnerability arises from incorrect permission assignments in the Universal Forwarder installation directory—by default, C:\Program Files\SplunkUniversalForwarder.

Non-administrator users on the affected machine can access and potentially modify all directory contents, which could be exploited for local privilege escalation or to compromise sensitive log data.

Permission Assignment and Exploitation Vector

This issue is classified under CWE-732: Incorrect Permission Assignment for Critical Resource.

During installation or upgrade, the Universal Forwarder sets overly permissive permissions, allowing users outside the Administrators group to access, modify, or replace files within the directory.

This misconfiguration can lead to several risks, including:

• Unauthorized modification of executable files or configurations
• Replacement of service binaries, potentially leading to arbitrary code execution with elevated privileges
• Exposure or tampering of sensitive log data

The problem is strictly local; remote exploitation is not possible without valid credentials and access to the affected machine.

No malware exploiting this vulnerability has been observed in the wild as of the latest update.

Technical Example: Permission Audit

Administrators can audit the directory permissions using the following command:

powershellicacls "C:\Program Files\SplunkUniversalForwarder"

If permissions such as (F) (Full Control) or (M) (Modify) are granted to non-administrator groups (e.g., BUILTIN\Users or EveryoneThe system is vulnerable.

Affected Versions, Mitigation, and Remediation

The following table summarizes affected and fixed versions:

Solution:
Upgrade Universal Forwarder for Windows to the respective fixed version or higher as indicated above.

Mitigation (if immediate upgrade is not possible):
Administrators should manually remove excessive permissions from the installation directory.

Run the following command as a system administrator:

texticacls.exe "<path\to\installation\directory>" /remove:g *BU /C

This command removes group permissions for BUILTIN\Users (*BU), restricting access to authorized administrators only.

Apply this mitigation in the following scenarios:

• Immediately after a new installation of an affected version
• After upgrading to an affected version
• After uninstalling and reinstalling an affected version

Security Best Practices and Next Steps

Splunk recommends always running the latest Universal Forwarder version and regularly auditing directory permissions after installation or upgrade.

Administrators should ensure that only trusted accounts (e.g., SYSTEM Administrators) have Full Control over the installation directory, and promptly apply vendor updates as they become available.

Organizations unable to upgrade immediately should implement the provided mitigation to reduce exposure, monitor systems for unauthorized changes, and review user privileges regularly.

References:

• Advisory ID: SVD-2025-0602
• CVE ID: CVE-2025-20298
• CWE: CWE-732
• Bug ID: VULN-27637

For more details and ongoing updates, consult the official Splunk security advisory portal.

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