Improper Input Validation through Protocol-Relative URL in Classic Dashboards in Splunk Enterprise

CVE-2026-20256

What is CVE-2026-20256?

In Splunk Enterprise versions below 10.2.4, 10.0.7, 9.4.12, and 9.3.13, and Splunk Cloud Platform versions below 10.3.2512.13, 10.2.2510.15, 10.1.2507.23, and 9.3.2411.132, a low-privileged user that does not hold the 'admin' or 'power' Splunk roles could cause data exfiltration through classic dashboards by redirecting a victim to an external site using a protocol-relative URL in a drill-down link.The vulnerability exists because the URL classifier in classic dashboards only recognizes http:// and https:// schemes when checking for external URLs. Protocol-relative URLs such as //attacker.com bypass this check entirely, and Splunk Web does not show the external-navigation warning dialog to the victim.

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