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

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 or tag the Marko runtime failed to prevent tag breakout when the closing tag used non-lowercase casing. An attacker...

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

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 or tag the Marko runtime failed to prevent tag breakout when the closing tag used non-lowercase casing. An attacker...

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

Summary When dynamic text is interpolated into a or 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 or block could break out of the tag with , , etc. and inject arbitrary HTML/JavaScript, resulting in...