# CVE-2026-20256: Improper Input Validation through Protocol-Relative URL in Classic Dashboards in Splunk Enterprise

> Low-privileged users can exfiltrate data by redirecting victims to external sites via protocol-relative URLs in Splunk dashboards, bypassing security warnings.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 10 Jun 2026
- **Updated:** 10 Jun 2026
- **Also known as:** GHSA-p326-4xf8-xp88

## What is CVE-2026-20256?

CVE-2026-20256 is a medium-severity vulnerability in Splunk Splunk, published on 10 Jun 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-20256?

It affects 2 products.


Products: Splunk Splunk, Splunk Splunk Cloud Platform.

## How do I fix CVE-2026-20256?

No fix has been published for CVE-2026-20256 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-20256 being exploited?

There is no known exploitation of CVE-2026-20256 in the wild and no public exploit code.

## Other vulnerabilities in Splunk Splunk

- [CVE-2026-20253](https://insights.sbomify.com/CVE-2026-20253/): Splunk Enterprise Missing Authentication for Critical Function (critical 9.8, exploited in the wild)
- [CVE-2026-76268](https://insights.sbomify.com/CVE-2026-76268/): Missing Authentication for Critical Function in the Patroni REST API in Splunk Enterprise (critical 9.8)
- [CVE-2026-76284](https://insights.sbomify.com/CVE-2026-76284/): Improper Neutralization in Splunk Enterprise (critical 9.8)
- [CVE-2026-76285](https://insights.sbomify.com/CVE-2026-76285/): Improper Adherence to Coding Standards in Splunk Enterprise (critical 9.8)
- [CVE-2017-17067](https://insights.sbomify.com/CVE-2017-17067/): Auth bypass in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20256 and fix it if it is affected.

What it is: CVE-2026-20256 is a medium-severity vulnerability in Splunk Splunk, published on 10 Jun 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-20256 in the wild and no public exploit code.

Affected product: Splunk Splunk. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-20256/ (Markdown: https://insights.sbomify.com/CVE-2026-20256/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20256
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20256
- OSV: https://osv.dev/vulnerability/CVE-2026-20256

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-20256/
Summaries are generated and may contain mistakes; the official description above is the record.