CVE-2026-20256: splunk Input Validation Flaw — Fix

Description

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.<br><br>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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CVSS v3.1 Score

5.7

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0025

Probability of exploitation

0.16%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-20 Improper Input Validation

Affected Products

Vendor	Product	Versions
splunk	splunk	9.3.0 — 9.3.13
splunk	splunk	9.4.0 — 9.4.12
splunk	splunk	10.0.0 — 10.0.7
splunk	splunk	10.2.0 — 10.2.4
splunk	splunk_cloud_platform	9.3.2411 — 9.3.2411.132
splunk	splunk_cloud_platform	10.1.2507 — 10.1.2507.23
splunk	splunk_cloud_platform	10.2.2510 — 10.2.2510.15
splunk	splunk_cloud_platform	10.3.2512 — 10.3.2512.13

References

Advisories & Patches

https://advisory.splunk.com/advisories/SVD-2026-0606

Frequently Asked Questions

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.<br><br>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. It has a CVSS v3.1 base score of 5.7 (MEDIUM).

How severe is CVE-2026-20256? +

CVE-2026-20256 has a CVSS v3.1 score of 5.7 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0025, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-20256? +

CVE-2026-20256 affects products from splunk, specifically: splunk, splunk_cloud_platform. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-20256? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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