CVE-2026-41591Public exploitNetwork attack vector

XSS via case-sensitive script and style escaping

Published May 8, 2026 · Updated May 8, 2026

Cross-site scripting in Marko before 5.38.36 and @marko/runtime-tags before 6.0.164 allows remote authenticated users to run JavaScript. Runtime escaping helpers use case-sensitive regular expressions, allowing mixed-case script or style closing tags to pass unchanged and terminate the browser context. Exploitation requires attacker-controlled data to be explicitly interpolated inside such a block and executes code in the page visitor's session.

CVSS severity6.4
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Cross-site scripting in Marko before 5.38.36 and @marko/runtime-tags before 6.0.164 allows remote authenticated users to run JavaScript. Runtime escaping helpers use case-sensitive regular expressions, allowing mixed-case script or style closing tags to pass unchanged and terminate the browser context. Exploitation requires attacker-controlled data to be explicitly interpolated inside such a block and executes code in the page visitor's session.

The record

CVE
CVE-2026-41591
Published
May 8, 2026
Updated
May 8, 2026
Vendor
Marko
Product
Marko
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 8, 2026CVE publishedPublication date reported by the CVE source.
  2. May 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=marko < 5.38.36
  2. Affected versionversion=@marko/runtime-tags < 6.0.164

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Marko · Markoversion=marko < 5.38.36; version=@marko/runtime-tags < 6.0.164

Published CVSS scores

6.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo