CVE-2025-20387 is a vulnerability affecting Splunk Universal Forwarder for Windows in versions below 10.0.2, 9.4.6, 9.3.8, and 9.2.10. The issue stems from the product assigning overly permissive access rights to the Universal Forwarder installation directory during new installations or upgrades. Specifically, non-administrator users on the local machine can gain read and write access to this directory and all its contents, which are security-critical resources. This misconfiguration allows unintended actors with limited privileges to potentially read sensitive configuration files, modify binaries or scripts, and thus compromise the forwarder's operation or escalate privileges. The vulnerability requires local access with low privileges and some user interaction, but no administrative rights are needed, making it easier for insider threats or malware with limited access to exploit. The CVSS 3.1 score of 8.0 reflects high impact on confidentiality, integrity, and availability, with low attack complexity and network vector. Although no public exploits are currently known, the vulnerability poses a significant risk to environments relying on Splunk Universal Forwarder for log collection and monitoring. The affected versions span multiple recent releases, indicating a broad exposure. The vulnerability was publicly disclosed on December 3, 2025, with no patch links provided yet, suggesting organizations must monitor vendor updates closely or implement interim mitigations.

For European organizations, this vulnerability can lead to unauthorized disclosure of sensitive log data, tampering with log forwarding processes, or disruption of monitoring capabilities, undermining security operations and compliance efforts. Attackers exploiting this flaw could manipulate logs to hide malicious activities or inject malicious code into the forwarder, potentially pivoting to other systems. Critical sectors such as finance, healthcare, energy, and government agencies that rely heavily on Splunk for security monitoring are at heightened risk. The compromise of log integrity and availability can delay incident detection and response, increasing the likelihood and impact of broader cyberattacks. Additionally, regulatory requirements under GDPR and NIS Directive emphasize protecting monitoring infrastructure, so exploitation could lead to legal and reputational consequences. The vulnerability's local attack vector means that insider threats or malware with limited privileges are primary concerns. Given the widespread use of Windows endpoints in European enterprises, the scope of affected systems is substantial.

Organizations should prioritize upgrading Splunk Universal Forwarder for Windows to versions 10.0.2, 9.4.6, 9.3.8, or 9.2.10 or later as soon as patches become available. Until patches are applied, administrators should manually audit and correct NTFS permissions on the Universal Forwarder installation directory to restrict access strictly to administrators and the Splunk service account. Employing endpoint protection solutions to detect and prevent unauthorized local privilege escalations or file modifications can reduce exploitation risk. Implement strict local user account management and limit the number of users with local access to Splunk servers. Monitoring file integrity of the installation directory and alerting on unexpected changes can provide early warning of exploitation attempts. Additionally, organizations should review and harden Splunk configurations to minimize the impact of potential compromise. Regularly reviewing logs for suspicious local user activity and conducting internal audits of Splunk deployments will help maintain security posture.