CVE-2026-20257 Overview
CVE-2026-20257 is an input validation vulnerability [CWE-20] in Splunk Enterprise and Splunk Cloud Platform. A low-privileged user without the admin or power Splunk roles can craft a classic dashboard that exfiltrates sensitive data from the browser of a higher-privileged user who views it. The flaw stems from incomplete validation of style attribute values in classic dashboard panels. This allows requests to reach external domains outside the configured Trusted Domains List. Exploitation requires social engineering to trick a privileged victim into rendering the malicious dashboard.
Critical Impact
A low-privileged Splunk user can exfiltrate sensitive browser data from higher-privileged victims, bypassing the Trusted Domains List enforcement.
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-2026-20257 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-20257
Vulnerability Analysis
The vulnerability resides in Splunk's classic dashboard panel rendering logic. Classic dashboards permit CSS styling through panel configuration, but the application does not fully validate the contents of style attribute values. An attacker authenticated as a low-privileged user can author a dashboard with crafted style properties that issue outbound requests at render time. These requests bypass the Trusted Domains List, which is the control intended to restrict dashboard-initiated traffic to vetted destinations.
When a higher-privileged user views the malicious dashboard, their browser executes the embedded styling, transmitting session-context data to attacker-controlled domains. The attacker can capture URL-encoded values, referer information, and other sensitive browser-side data tied to the victim's privileged session.
Root Cause
The root cause is improper input validation [CWE-20] of CSS style attribute values inside classic dashboard panel definitions. The Trusted Domains List enforcement does not inspect URLs embedded within style values, leaving an unsanitized sink that reaches external network resources during dashboard rendering.
Attack Vector
Exploitation is network-based and requires both privileges and user interaction. The attacker must hold a valid Splunk account without admin or power roles. The attacker authors a classic dashboard containing crafted style values and then phishes a higher-privileged user into viewing the dashboard. Because exploitation depends on the victim initiating the request, the low-privileged user cannot trigger the vulnerability at will.
No verified proof-of-concept code has been published. See the Splunk Security Advisory SVD-2026-0607 for vendor technical details.
Detection Methods for CVE-2026-20257
Indicators of Compromise
- Classic dashboards created by non-admin, non-power users containing unusual inline style attributes referencing external URLs.
- Outbound HTTP requests from privileged user browsers to domains not present in the Splunk Trusted Domains List during dashboard rendering.
- Phishing messages or internal links directing privileged users to view dashboards authored by lower-privileged accounts.
Detection Strategies
- Audit data/ui/views REST endpoint activity for new or modified classic dashboards created by non-privileged roles.
- Parse stored dashboard XML for style attributes containing url(...) references or external HTTP/HTTPS endpoints.
- Review Splunk web access logs for dashboard view events followed by anomalous referer traffic to external hosts.
Monitoring Recommendations
- Enable and review Splunk's _audit index for dashboard creation and modification events tied to low-privileged accounts.
- Forward web proxy and browser telemetry to a central analytics platform to correlate dashboard render events with outbound domain requests.
- Alert on any dashboard-initiated requests that bypass or fall outside the configured Trusted Domains List.
How to Mitigate CVE-2026-20257
Immediate Actions Required
- Upgrade Splunk Enterprise to 10.2.4, 10.0.7, 9.4.12, 9.3.13, or later as appropriate for your release line.
- Confirm Splunk Cloud Platform instances are running 10.3.2512.13, 10.2.2510.15, 10.1.2507.23, or 9.3.2411.132 or later.
- Inventory existing classic dashboards authored by non-admin, non-power users and review them for suspicious style attributes.
Patch Information
Splunk has released fixed versions addressing CVE-2026-20257. Administrators should review the Splunk Security Advisory SVD-2026-0607 for the full list of patched releases and upgrade guidance. Splunk Cloud Platform tenants receive updates managed by Splunk, but operators should verify their tenant version against the patched baselines.
Workarounds
- Restrict dashboard creation privileges to trusted roles where operationally feasible until patching is complete.
- Tighten the Trusted Domains List and educate privileged users to avoid viewing dashboards from untrusted authors.
- Apply role-based access controls to limit which users can publish or share classic dashboards across the deployment.
# Verify your Splunk Enterprise version against the patched baseline
$SPLUNK_HOME/bin/splunk version
# Review classic dashboards for suspicious style attributes
grep -r -E 'style="[^"]*url\(' $SPLUNK_HOME/etc/apps/*/local/data/ui/views/
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
