CVE-2025-20387 is a vulnerability affecting Splunk Universal Forwarder for Windows versions below 10.0.2, 9.4.6, 9.3.8, and 9.2.10. The issue stems from improper permission settings on the Universal Forwarder installation directory following a fresh install or upgrade. Specifically, the directory and its contents are assigned permissions that allow non-administrator users on the local machine to access and potentially modify files that should be restricted. This misconfiguration can expose security-critical resources, enabling unauthorized actors with limited privileges to read sensitive data or alter configuration and executable files. Such unauthorized modifications could lead to privilege escalation, data leakage, or disruption of Splunk's logging and monitoring capabilities. The vulnerability requires local access with limited privileges and user interaction during installation or upgrade, which somewhat limits remote exploitation but still poses a significant risk in multi-user or shared environments. The CVSS v3.1 score of 8.0 reflects the high impact on confidentiality, integrity, and availability, combined with low attack complexity and limited privileges required. Although no active exploits are reported, the vulnerability's nature makes it a critical concern for organizations relying on Splunk Universal Forwarder on Windows systems. Remediation involves updating to fixed versions (10.0.2, 9.4.6, 9.3.8, or 9.2.10) and auditing file system permissions post-installation or upgrade to ensure proper access controls are enforced.

The vulnerability can lead to unauthorized disclosure of sensitive log data, unauthorized modification of Splunk configuration or executable files, and potential disruption of log forwarding services. This compromises the confidentiality, integrity, and availability of the Splunk Universal Forwarder, which is critical for security monitoring and incident response. Attackers with local access but limited privileges could exploit this to escalate privileges or tamper with security monitoring data, undermining trust in security operations. Organizations relying on Splunk for centralized logging and security analytics may face increased risk of undetected intrusions or data breaches. The impact is especially severe in environments where multiple users share the same Windows system or where endpoint security is critical. Additionally, the vulnerability may facilitate lateral movement or persistence by adversaries who gain limited local access. Overall, the threat undermines the security posture of affected organizations and could lead to regulatory compliance issues if sensitive data is exposed or logs are manipulated.

1. Immediately upgrade Splunk Universal Forwarder for Windows to versions 10.0.2, 9.4.6, 9.3.8, or 9.2.10 where the vulnerability is fixed. 2. After installation or upgrade, manually verify and correct NTFS permissions on the Universal Forwarder installation directory to restrict access strictly to administrators and the Splunk service account. 3. Implement strict local user account management policies to limit the number of users with local access on systems running Splunk Universal Forwarder. 4. Use application whitelisting and endpoint protection to detect unauthorized modifications to Splunk files. 5. Monitor file integrity of Splunk installation directories using host-based intrusion detection systems (HIDS). 6. Educate system administrators to be cautious during upgrades and to validate permissions post-upgrade. 7. Where possible, isolate Splunk Universal Forwarder hosts to minimize exposure to untrusted users. 8. Review and harden Windows security policies related to file system permissions and user rights assignments. 9. Maintain up-to-date backups of Splunk configurations and logs to enable recovery in case of tampering.