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Description

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.

PUBLISHED Reserved 2026-04-21 | Published 2026-05-08 | Updated 2026-05-08 | Assigner GitHub_M




MEDIUM: 6.4CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Problem types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Product status

marko < 5.38.36
affected

@marko/runtime-tags < 6.0.164
affected

References

github.com/.../marko/security/advisories/GHSA-x9fj-57fh-c8wq exploit

github.com/.../marko/security/advisories/GHSA-x9fj-57fh-c8wq

cve.org (CVE-2026-41591)

nvd.nist.gov (CVE-2026-41591)

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