medium6.4
CVE-2026-41591
Marko: XSS via case-insensitive script/style closing tag bypass in runtime HTML escaping
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | marko | < 5.38.36 | 5.38.36 |
| npm | @marko/runtime-tags | < 6.0.164 | 6.0.164 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Openjsf | Marko | before 5.38.36 |
| Openjsf | Marko\/Runtime-Tags | before 6.0.164 |