CVE-2026-41591 — Marko: XSS via case-insensitive script/style closing tag bypass in runtime HTML escaping

Affected: marko-js marko

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.

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CVE-2026-41591 — Marko: XSS via case-insensitive script/style closing tag bypass in runtime HTML escaping