CVE-2025-20298 - How Weak Directory Permissions in Splunk Universal Forwarder for Windows Expose Your Data

CVE-2025-20298 is a security vulnerability discovered in Splunk Universal Forwarder for Windows. Versions *below* 9.4.2, 9.3.4, 9.2.6, and 9.1.9 (yes, all those branches!) have a critical misconfiguration: after a new install or an upgrade, directory permissions on
C:\Program Files\SplunkUniversalForwarder
are incorrectly assigned, so that even non-admin users can access it fully.

Why Does This Happen?

During installation or upgrade, the Universal Forwarder should set its folder permissions so that only Administrators (or the SYSTEM user) can access or modify files. Instead, these older versions use permissions that allow ANY logged-in user on the machine to read, write, or even delete contents within that folder. That’s a serious security hole.

How an Attacker Can Exploit This

All an attacker needs is access to a Windows user account (even local, low-privilege) to access the Splunk Universal Forwarder directory. If they can write files there, they might plant a malicious DLL or EXE, or tamper with configuration to hijack service behavior.

You can check directory permissions using PowerShell

Get-Acl "C:\Program Files\SplunkUniversalForwarder" | Format-List

What you DON'T want to see:
- Users like Authenticated Users, Everyone, or regular <DOMAIN>\Users with Modify or FullControl rights.

You should only see Administrators, SYSTEM, or the custom Splunk service account with full access.

If the Splunk Universal Forwarder uses any startup scripts

echo 'Write-Output "pwned!"' > "C:\Program Files\SplunkUniversalForwarder\bin\evil.ps1"

You (the attacker) edit scripts or binaries here, and when Splunk runs them as SYSTEM, your code runs with elevated privileges.

9.1.9 or above

Official downloads:
- Splunk Universal Forwarder Download (Official site)

After patching, fix existing permissions

icacls "C:\Program Files\SplunkUniversalForwarder" /inheritance:r /grant "Administrators:F" /grant "SYSTEM:F" /remove "Users" "Authenticated Users" "Everyone" /t

3. Regularly Audit

Set up a scheduled script to check for improper permissions on critical system folders.

References

- Splunk Security Advisory – Incorrect Directory Permissions (CVE-2025-20298)
- NIST NVD: CVE-2025-20298
- Splunk Universal Forwarder Documentation


Summary:
CVE-2025-20298 is a textbook case of why installation scripts must set strong permissions on application folders—don’t let non-admins near your software! Patch your Splunk Universal Forwarder ASAP and always check those permissions. If you need a quick-fix script or help securing your systems, let us know in the comments. Stay safe!

Timeline

Published on: 06/02/2025 18:15:23 UTC
Last modified on: 06/04/2025 14:54:53 UTC