CVE-2026-41591: marko-js marko Cross-site Scripting

Vulnerability summary

CVE-2026-41591 is a medium (CVSS 6.4) Cross-site Scripting vulnerability in marko-js marko. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 17.2% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 08-05-2026
   PublishedVulnerability first disclosed.
2. 08-05-2026
   Last modifiedVulnerability information updated.

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.

• CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.