CVE-2026-20138 is a vulnerability identified in multiple versions of Splunk Enterprise prior to 10.2.0, 10.0.2, 9.4.7, 9.3.9, and 9.2.11. The issue arises in Search Head Cluster (SHC) deployments where users holding roles with access to the Splunk _internal index can view sensitive authentication secrets—specifically integrationKey, secretKey, and appSecretKey—generated by the Duo Two-Factor Authentication app for Splunk. These secrets are logged in plaintext within internal logs, violating secure logging practices (CWE-532). Since these keys are critical for the Duo 2FA mechanism, their exposure could allow an attacker with legitimate access to the _internal index to compromise the multi-factor authentication process, potentially leading to unauthorized access to Splunk environments or downstream systems. The vulnerability requires authenticated access with elevated privileges but no further user interaction, making it a significant risk in environments where internal access controls are weak or compromised. The CVSS 3.1 score of 6.8 reflects medium severity, with high impact on confidentiality, integrity, and availability, but limited attack vector (adjacent network) and requiring privileges. No public exploits are currently known, but the presence of sensitive secrets in logs is a critical security misconfiguration that should be remediated promptly.

For European organizations, the exposure of Duo 2FA secrets within Splunk logs can severely undermine the security of authentication mechanisms protecting critical monitoring and analytics infrastructure. This can lead to unauthorized access to Splunk environments, enabling attackers to manipulate logs, exfiltrate sensitive data, or disrupt monitoring capabilities, impacting incident detection and response. Sectors such as finance, healthcare, government, and critical infrastructure that rely heavily on Splunk for security monitoring and compliance are particularly at risk. The compromise of multi-factor authentication secrets could facilitate lateral movement within networks, increasing the scope and severity of breaches. Additionally, regulatory compliance frameworks in Europe, such as GDPR, impose strict requirements on protecting sensitive information, and such a vulnerability could lead to significant legal and reputational consequences if exploited.

European organizations should immediately upgrade Splunk Enterprise to versions 10.2.0, 10.0.2, 9.4.7, 9.3.9, or 9.2.11 or later where this vulnerability is patched. Until upgrades are applied, restrict access to the _internal index strictly to only trusted administrators and audit all roles with such access. Implement strict role-based access controls (RBAC) and monitor for unusual access patterns to the _internal index. Review and sanitize log configurations to ensure sensitive keys are not logged in plaintext. Consider rotating Duo 2FA integration keys after patching to invalidate any potentially exposed secrets. Additionally, enhance monitoring for suspicious activities related to authentication and internal log access. Engage with Splunk support or Duo documentation for any recommended configuration changes to minimize secret exposure. Finally, conduct security awareness training for administrators on the risks of sensitive data exposure in logs.