CVE-2025-20389: 
Splunk Enterprise vulnerability analysis and mitigation

CVE-2025-20389 is an improper input validation vulnerability in the Splunk Secure Gateway app that allows a low-privileged user to craft a malicious payload via the label column field when adding a new device, potentially causing a client-side denial of service (DoS). It affects Splunk Enterprise versions below 10.0.2, 9.4.6, 9.3.8, and 9.2.10, as well as Splunk Secure Gateway app versions below 3.9.10, 3.8.58, and 3.7.28 on Splunk Cloud Platform. The vulnerability was disclosed on December 3, 2025, with patches released the same day (Splunk Advisory). It carries a CVSS v3.1 base score of 6.5 (Medium) per NVD, and 4.3 (Medium) per the CNA (Cisco Systems) (Splunk Advisory).

The vulnerability is classified as CWE-20 (Improper Input Validation), stemming from insufficient sanitization of user-supplied input in the label column field of the Splunk Secure Gateway app's device management interface (Splunk Advisory). An authenticated low-privileged user — one who does not hold the "admin" or "power" Splunk roles — can submit a crafted malicious payload through this field after adding a new device, which is then processed client-side without adequate validation. The attack vector is network-based, requires low privileges, low attack complexity, and no user interaction, with the impact confined to availability (client-side DoS). No public proof-of-concept code has been identified (Splunk Advisory).

Successful exploitation results in a client-side denial of service, disrupting the availability of the Splunk Secure Gateway app and potentially the broader Splunk Enterprise interface for affected users. There is no impact on confidentiality or integrity — sensitive data is not exposed and no unauthorized modifications can be made through this vulnerability (Splunk Advisory). The scope of impact is limited to the client-side application experience and does not enable lateral movement or remote code execution.

There is no known public proof-of-concept exploit and no evidence of active in-the-wild exploitation as of the disclosure date (Splunk Advisory). The EPSS score is approximately 0.043%, indicating a very low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported.

1. Authentication: Log in to a Splunk Enterprise or Splunk Cloud Platform instance using a low-privileged account (one without "admin" or "power" roles).
2. Navigate to Splunk Secure Gateway: Access the Splunk Secure Gateway app within the Splunk interface.
3. Add a new device: Initiate the process of adding a new device within the app, which presents the device registration form including the label column field.
4. Inject malicious payload: Enter a crafted malicious payload into the label field — this could be an oversized string, specially formatted input, or other content designed to trigger improper client-side processing.
5. Trigger client-side DoS: Submit the form; the malicious label value is stored and subsequently rendered client-side without proper validation, causing the client application to become unresponsive or crash for users who view the affected device listing (Splunk Advisory).

• Logs: Splunk internal logs showing unusual or oversized values submitted to the device label field via the Secure Gateway app; audit log entries from low-privileged accounts performing device additions with anomalous label content.
• Application Behavior: Client-side browser crashes or unresponsiveness when loading the Splunk Secure Gateway device list for users other than the one who submitted the payload.
• Splunk Search: Query index=_audit action=add_device or review Secure Gateway app activity logs for unexpected or malformed label field values submitted by non-admin accounts.

Splunk has released patched versions addressing this vulnerability: Splunk Enterprise 10.0.2, 9.4.6, 9.3.8, and 9.2.10; and Splunk Secure Gateway app versions 3.9.10, 3.8.58, and 3.7.28 for Splunk Cloud Platform (Splunk Advisory). Organizations should upgrade to the fixed versions as the primary remediation. As interim mitigations, administrators can restrict access to the Splunk Secure Gateway app to trusted users only, monitor device label fields for unusual input, and apply the principle of least privilege to limit which accounts can add devices.

Heise reported on the December 2025 Splunk security patch batch, noting that unauthorized access scenarios were addressed across multiple CVEs in the release. No significant independent researcher commentary or social media discussion specific to CVE-2025-20389 has been identified, consistent with its moderate severity and limited exploitation potential.