CISA KEV: Splunk Enterprise Missing Authentication (CVE-2026-20253)

Splunk Enterprise is affected by CVE-2026-20253, a critical missing authentication vulnerability in its PostgreSQL sidecar service endpoint. This flaw allows an unauthenticated attacker to create or truncate arbitrary files on the underlying system. Published on June 18, 2026, and added to CISA's Known Exploited Vulnerabilities Catalog, this vulnerability poses a significant risk to organizations running vulnerable Splunk Enterprise instances. Exploitation can lead to severe denial of service, data integrity issues, and potentially serve as a stepping stone for further system compromise if critical configuration files or executables are targeted. Defenders must prioritize immediate mitigation to prevent unauthorized file manipulation and potential system instability.

Attack Chain

1. Initial Access: An unauthenticated attacker identifies a vulnerable Splunk Enterprise instance with an exposed PostgreSQL sidecar service endpoint.
2. Vulnerability Exploitation: The attacker sends specially crafted requests to the accessible PostgreSQL sidecar service endpoint.
3. Missing Authentication Bypass: Due to CVE-2026-20253, the service endpoint fails to properly authenticate the attacker's requests, granting unauthorized access to critical functions.
4. Arbitrary File Creation: The attacker leverages this unauthenticated access to create new, arbitrary files on the underlying operating system where Splunk Enterprise is running.
5. Arbitrary File Truncation: The attacker can also use the exploit to truncate (empty) existing arbitrary files, potentially including critical system or Splunk application files.
6. Impact and Potential Escalation: Manipulation of files can lead to denial of service by rendering the system inoperable, data corruption, or serve as a vector for achieving persistence or remote code execution by modifying sensitive configurations or injecting malicious executables.

Impact

The direct impact of CVE-2026-20253 is the ability for an unauthenticated attacker to create or truncate arbitrary files on the affected system. This can lead to severe denial of service by overwriting or emptying critical operating system or Splunk Enterprise application files, causing system instability or complete outage. While specific victim counts or targeted sectors are not detailed, any organization utilizing vulnerable Splunk Enterprise instances exposed to unauthenticated access is at risk. If an attacker can manipulate sensitive files (e.g., executables, configuration files), this could enable further compromise, potentially leading to remote code execution, data exfiltration, or the installation of persistent backdoors.

Recommendation

• Apply mitigations immediately in accordance with the vendor advisory SVD-2026-0603 for CVE-2026-20253.
• Ensure compliance with CISA's BOD 26-04 guidance, prioritizing patches for internet-facing instances of Splunk Enterprise.
• Implement network segmentation or access control lists to restrict unauthenticated access to the PostgreSQL sidecar service endpoint.
• Deploy the Sigma rules provided in this brief to your SIEM solution to detect suspicious file operations or process creations originating from the PostgreSQL sidecar service.