CVE-2026-20254: Splunk Enterprise Auth Bypass Vulnerability

CVE-2026-20254 Overview

CVE-2026-20254 affects Splunk Enterprise and Splunk Cloud Platform. A low-privileged user without the admin or power Splunk roles can craft a malicious classic dashboard. When a higher-privileged user views the dashboard, attackers can exfiltrate sensitive data to an external server. The flaw bypasses the external content restriction through a Cascading Style Sheets (CSS) injection. The Trusted Domains security check does not fully validate inline style attribute values, enabling outbound requests to untrusted domains and credential exfiltration. The vulnerability is classified under [CWE-20] Improper Input Validation.

Critical Impact
A low-privileged Splunk user can stage a malicious classic dashboard that exfiltrates sensitive data when a higher-privileged victim views it.

Affected Products

Splunk Enterprise versions below 10.2.4, 10.0.7, 9.4.12, and 9.3.13
Splunk Cloud Platform versions below 10.3.2512.13, 10.2.2510.15, and 10.1.2507.23
Splunk Cloud Platform versions below 9.3.2411.132

Discovery Timeline

2026-06-10 - CVE-2026-20254 published to NVD
2026-06-10 - Last updated in NVD database

Technical Details for CVE-2026-20254

Vulnerability Analysis

The vulnerability resides in Splunk's classic dashboard rendering pipeline. Splunk applies a Trusted Domains security check designed to restrict outbound content references to approved hosts. The check does not fully validate values inside inline style attributes. Attackers can embed CSS directives that reference external URLs, causing the browser to issue requests to attacker-controlled servers when a victim renders the dashboard.

Because the request originates from an authenticated session, the attacker can capture data reflected in the dashboard context, including identifiers, tokens, or query results visible to the higher-privileged viewer. This pattern of CSS-based data exfiltration is a known web bypass technique against content restriction logic.

Root Cause

The root cause is incomplete input validation [CWE-20] in the Trusted Domains check. The validator inspects standard HTML elements and source attributes but does not parse and sanitize CSS expressions inside inline style attributes. Crafted CSS values such as url() references slip through, enabling the browser to fetch resources from arbitrary external hosts.

Attack Vector

The attack requires an authenticated low-privileged Splunk user and a victim with higher privileges who opens the malicious classic dashboard. The attacker authors a dashboard containing crafted inline CSS that triggers outbound requests when rendered. When an admin or power role user views the dashboard, the browser issues attacker-directed requests carrying contextual data. Refer to the Splunk Security Advisory SVD-2026-0604 for vendor-published technical detail.

Detection Methods for CVE-2026-20254

Indicators of Compromise

Outbound HTTP or HTTPS connections from Splunk Web user browsers to unfamiliar external domains during dashboard rendering.
Classic dashboards created or modified by non-admin, non-power users containing inline style attributes with url() references.
Splunk audit log entries showing dashboard edits by low-privileged users followed by views from privileged accounts.

Detection Strategies

Inspect dashboard XML and HTML source for inline style attributes containing external url() values or unexpected CSS imports.
Correlate dashboard view events in Splunk's _audit index with proxy or network telemetry showing requests to untrusted domains.
Hunt for new or recently modified data/ui/views objects authored by users lacking admin or power roles.

Monitoring Recommendations

Enable and centralize Splunk Web access and audit logs, and forward them to your SIEM for correlation with egress proxy logs.
Alert on dashboard modifications by low-privileged users and on first-time outbound destinations referenced by Splunk Web sessions.
Track high-privileged users viewing dashboards owned by lower-privileged authors as a triage signal.

How to Mitigate CVE-2026-20254

Immediate Actions Required

Upgrade Splunk Enterprise to 10.2.4, 10.0.7, 9.4.12, 9.3.13, or later as applicable to your release train.
Confirm Splunk Cloud Platform instances are on 10.3.2512.13, 10.2.2510.15, 10.1.2507.23, 9.3.2411.132, or later.
Audit existing classic dashboards authored by non-admin, non-power users for malicious inline CSS before privileged users open them.

Patch Information

Splunk has released fixed builds for both Splunk Enterprise and Splunk Cloud Platform. Apply the vendor-recommended versions listed in the Splunk Security Advisory SVD-2026-0604. Splunk Cloud Platform customers receive updates through the managed service maintenance schedule.

Workarounds

Restrict dashboard creation and editing capabilities to trusted roles by reviewing and tightening Splunk role capabilities such as edit_dashboards.
Require privileged users to avoid opening dashboards authored by untrusted accounts until patches are applied.
Enforce egress filtering on networks hosting Splunk Web users to limit outbound destinations to known-good domains.

bash

# Verify installed Splunk Enterprise version against fixed releases
$SPLUNK_HOME/bin/splunk version

# Review dashboards authored by non-admin, non-power users
$SPLUNK_HOME/bin/splunk search 'index=_audit action=edit object_category=view NOT (user IN (admin_users power_users))' -auth admin:<password>