High-Severity Vulnerability in Splunk Universal Forwarder for Windows (CVE-2025-20298)
June 11th, 2025
Severity Level: High
Technical Details
Vulnerability ID: CVE‑2025‑20298.
Component Affected: Universal Forwarder Versions 9.4.2, 9.3.4, 9.2.6, and 9.1.9.
Vulnerability Type: CWE‑732 - Incorrect Permission Assignment.
Exploitability: Local (requires low-level user privileges) but rated AV: N due to network-adjacent install/update mechanisms.
Discovery Date: May 2025.
Reported By: External security researchers in coordination with the Splunk Security Team.
The vulnerability originates from insecure default file permissions assigned to the Splunk Universal Forwarder for Windows installation directory. During installations or upgrades, the directory at C:\Program Files\SplunkUniversalForwarder may be assigned overly permissive access rights, enabling non-administrative users to read, write, or modify its contents.
This misconfiguration could allow a local, low-privileged attacker to replace executable files or inject malicious content into the installation directory. If malicious content is executed by the Splunk service, which typically runs with SYSTEM-level privileges, this could result in a complete system compromise without requiring administrative access or remote exploitation.
Our Cyber Threat Intelligence Unit recently identified a significant vulnerability (CVE-2025-20298) in the Splunk Universal Forwarder for Windows. This flaw enables local privilege escalation due to improper permissions being set during installation or upgrades. It impacts several major version branches and carries a ‘High’ severity rating (CVSS 8.0). Successful exploitation could allow non-administrator users to access and modify all files within the installation directory, posing a serious risk to system integrity and security.
Impact
Successful exploitation of CVE-2025-20298 can allow local attackers to:
Read, modify, or replace executable files within the Splunk Universal Forwarder installation directory.
Gain SYSTEM-level privileges by executing malicious code under the context of a privileged Splunk service.
Tamper with log forwarding, audit trails, or agent behavior, potentially bypassing monitoring systems.
The elevated privileges of the Splunk Forwarder and its essential role in security monitoring make this vulnerability a significant risk for enterprise environments, particularly in organizations with widespread deployments and delayed patch management. If left unaddressed, this flaw could be exploited by attackers to move laterally within the network, establish persistence, or completely compromise the host system.
Detection Method
To determine if a system is affected:
Check the Splunk Universal Forwarder Version: Navigate to the Splunk UF installation directory and verify the installed version using the command line or version file (e.g., \splunk version or through Windows "Programs and Features").
Affected Versions: Systems running versions prior to 9.4.2, 9.3.4, 9.2.6, or 9.1.9 are vulnerable to CVE-2025-20298.
Mitigation Status: Systems running versions 9.4.2, 9.3.4, 9.2.6, or 9.1.9 (or later) are patched and are no longer vulnerable to this issue.
Security monitoring systems should look for:
Excessively permissive access rights to the Splunk Universal Forwarder installation directory.
Execution of unexpected binaries or modified files in C:\Program Files\SplunkUniversalForwarder.
The use of icacls or forensic tools can reveal improper ACLs assigned to non-administrative users..
File integrity violations, such as unauthorized writes or creation of executables in Splunk directories.
Splunk service anomalies, such as forwarders spawning unknown processes or child scripts.
Indicators of Compromise
There are no Indicators of Compromise (IOCs) for this advisory.
Recommendations
Immediate Update: All users must upgrade the Splunk Universal Forwarder for Windows to versions 9.4.2, 9.3.4, 9.2.6, or 9.1.9, depending on their current deployment branch.
Enterprise Patch Deployment: Organizations should prioritize and expedite the rollout of these updates across all affected endpoints by utilizing centralized patch management systems..
Permission Hardening (Interim Mitigation): If immediate upgrades are not feasible, administrators should manually correct file system permissions using the following command: [ icacls "C:\Program Files\SplunkUniversalForwarder" /remove:g *BU /C ]. This removes modify access for non-administrator users (BUILTIN\Users).
Monitor File Integrity: Implement file integrity monitoring (FIM) on the Splunk installation directory to identify unauthorized changes or malicious file injections.
Privilege Segregation: Configure Splunk services to operate under the principle of least privilege for service accounts instead of SYSTEM whenever possible, to reduce the impact of potential exploitation.
Conclusion
CVE-2025-20298 is a critical local privilege escalation vulnerability affecting the Splunk Universal Forwarder. If exploited, it could compromise system integrity and undermine enterprise observability. All affected versions should be treated as vulnerable until properly patched and access control lists (ACLs) are updated. Prompt action is strongly recommended to mitigate this threat, particularly in environments that depend on Splunk for monitoring critical infrastructure.