CVE-2025-20389 is a vulnerability identified in Splunk Enterprise versions prior to 10.0.2, 9.4.6, 9.3.8, and 9.2.10, as well as in the Splunk Secure Gateway app versions below 3.9.10, 3.8.58, and 3.7.28 on the Splunk Cloud Platform. The root cause is improper or absent validation of input data in the 'label' column field when a new device is added via the Secure Gateway app. This flaw allows a low-privileged user—who does not possess the 'admin' or 'power' roles—to craft a malicious payload that manipulates the control or data flow within the client application. The primary consequence is a client-side denial of service (DoS), which disrupts the availability of the client interface or functionality. The vulnerability is remotely exploitable over the network without requiring user interaction, but it requires the attacker to have at least low-level privileges within the Splunk environment. The CVSS v3.1 base score is 4.3, indicating medium severity, with attack vector as network, low attack complexity, low privileges required, no user interaction, and impact limited to availability. No known active exploits have been reported, but the presence of this vulnerability could be leveraged in targeted attacks to disrupt monitoring or security operations. The vulnerability highlights the importance of rigorous input validation in security-critical applications like Splunk, which are widely used for log aggregation, monitoring, and security information and event management (SIEM).

For European organizations, the impact of CVE-2025-20389 primarily concerns availability disruptions in Splunk client interfaces or functionalities due to client-side denial of service. Splunk is extensively used across Europe in sectors such as finance, telecommunications, government, and critical infrastructure for security monitoring and operational intelligence. A successful exploitation could temporarily impair the ability of security teams to monitor and respond to incidents, potentially delaying detection of other threats. While the vulnerability does not compromise data confidentiality or integrity, the denial of service could degrade operational efficiency and incident response capabilities. Organizations with distributed Splunk deployments or those relying heavily on the Secure Gateway app for device onboarding are more vulnerable. The requirement for low privileges reduces the barrier for insider threats or compromised accounts to exploit this issue. Given the critical role of Splunk in security operations, even temporary disruptions can have cascading effects on organizational security posture and compliance with regulatory requirements such as GDPR.

To mitigate CVE-2025-20389, European organizations should promptly upgrade affected Splunk Enterprise versions to 10.0.2, 9.4.6, 9.3.8, or 9.2.10 or later, and update the Splunk Secure Gateway app to versions 3.9.10, 3.8.58, or 3.7.28 or later. Until patches are applied, restrict low-privileged user capabilities to add devices or manipulate the 'label' field within the Secure Gateway app. Implement strict input validation and sanitization controls on client-side inputs, especially for fields that influence control or data flow. Monitor Splunk logs for unusual activity related to device additions or malformed inputs. Employ network segmentation and access controls to limit exposure of Splunk management interfaces to trusted users only. Conduct regular audits of user roles and permissions to minimize the number of accounts with device addition privileges. Additionally, consider deploying client-side protections such as browser security policies or endpoint monitoring to detect and prevent client-side DoS conditions. Finally, maintain an incident response plan that includes procedures for handling Splunk service disruptions.