---
id: CVE-2026-41591
title: 'Marko is a declarative, HTML-based language for building web apps'
summary: >-
  Marko is a declarative, HTML-based language for building web apps. Prior to
  marko version 5.38.36 and prior to @marko/runtime-tags 6.0.164, when dynamic
  text is interpolated into a <script> or <style> tag the Marko runtime failed
  to prev…
severity: medium
cvss: 6.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N'
cwe:
  - CWE-79
vendor: openjsf
product: marko
affected:
  - marko < 5.38.36
  - marko/runtime-tags < 6.0.164
patched:
  - marko 5.38.36
  - marko/runtime-tags 6.0.164
published: '2026-05-08'
updated: '2026-08-26'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-41591'
references:
  - url: 'https://github.com/marko-js/marko/security/advisories/GHSA-x9fj-57fh-c8wq'
    label: security-advisories@github.com
  - url: 'https://github.com/marko-js/marko/security/advisories/GHSA-x9fj-57fh-c8wq'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00227
epssPercentile: 0.13659
ingestedAt: '2026-08-27T14:02:54.021Z'
---

## Overview

Marko is a declarative, HTML-based language for building web apps. Prior to marko version 5.38.36 and prior to @marko/runtime-tags 6.0.164, when dynamic text is interpolated into a <script> or <style> tag the Marko runtime failed to prevent tag breakout when the closing tag used non-lowercase casing. An attacker able to place input inside a <script> or <style> block could break out of the tag with </SCRIPT>, </Style>, etc. and inject arbitrary HTML/JavaScript, resulting in cross-site scripting. This issue has been patched in marko version 5.38.36 and @marko/runtime-tags 6.0.164.

## Affected

- `marko < 5.38.36`
- `marko/runtime-tags < 6.0.164`

## Remediation

Upgrade past the affected range:

- `marko 5.38.36`
- `marko/runtime-tags 6.0.164`