CVE-2026-41591 json
Marko: XSS via case-insensitive script/style closing tag bypass in runtime HTML escaping
published 6mo ago modified 2mo ago also GHSA-x9fj-57fh-c8wq , EUVD-2026-28790
- cvss
- 6.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 13%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- npm marko 5.38.36
- npm @marko/runtime-tags 6.0.164
- openjsf marko 5.38.36
- openjsf marko/runtime-tags 6.0.164
Is CVE-2026-41591 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 6mo ago
Exploit prediction
0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-09).
Exploits and checks
- github.com https://github.com/marko-js/marko/security/advisories/GHSA-x9fj-57fh-c8wq referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 6.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N |
| GitHub | 3.1 | 6.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N |
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
- marko-js marko
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
github.com
/marko-js/marko/security/advisories/GHSA-x9fj-57fh-c8wq
exploit, web, mitigation, patch, vendor-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-41591
advisory
-
github.com
/marko-js/marko
package
Sources
- CVE List CVE-2026-41591
- GitHub Advisory GHSA-x9fj-57fh-c8wq
- NVD CVE-2026-41591
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.