# CVE-2026-41149: Mermaid HTML injection in state diagram classDef

Source: https://junglewise.ai/threats/cve-2026-41149-mermaid-html-injection-in-state-diagram-classdef  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-22. Updated: 2026-06-09  
License: CC BY 4.0 with a link back

CVE-2026-41149 · Severity: medium · CVSS 4 · Published 2026-05-22

Mermaid is a popular library used to generate charts and diagrams from text. A vulnerability in how it handles state diagrams allows an attacker to inject malicious HTML code into a page. While the library attempts to block scripts, an attacker could still alter the visual appearance of the page or overlay fake content to deceive users.

Technologies: [mermaid (npm)](https://junglewise.ai/threats/technologies/mermaid). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-41149 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-41149 being exploited in the wild.

**How severe is CVE-2026-41149?** Medium severity, with a CVSS score of 4, published 22 May 2026.

**Which products and versions are affected?** mermaid (npm) SEMVER:introduced=11.0.0-alpha.1,fixed=11.15.0.

**Is there a fix for CVE-2026-41149?** Yes. mermaid (npm): upgrade to 11.15.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-41149 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-41149?** Check whether you run mermaid (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- mermaid (npm): upgrade to 11.15.0 or later

  ```sh
  npm install mermaid@11.15.0
  ```


## Technical details

An HTML injection vulnerability exists in Mermaid's state diagram implementation due to improper sanitization of the `classDef` directive. By crafting a specific diagram string, an attacker can use CSS and HTML tags to escape the SVG container and inject arbitrary DOM elements into the host page. While Mermaid's default configuration removes `<script>` tags (preventing direct XSS), an attacker can still perform UI redressing or CSS-based attacks. The vulnerability is exploitable if a user views a diagram containing malicious `classDef` definitions. Patches are available in versions 11.15.0 and 10.9.6; a workaround is to set `securityLevel` to `sandbox`.

## Affected products

- mermaid-js mermaid >= 11.0.0-alpha.1, <= 11.14.0
- mermaid-js mermaid <= 10.9.5

## Identifiers

- CVE-2026-41149
- GHSA-ghcm-xqfw-q4vr

## Timeline

- 2026-05-11: disclosed
- 2026-05-11: advisory
- 2026-05-11: patched

## References

- [https://api.github.com/users/zsxsoft](https://api.github.com/users/zsxsoft)
- [https://github.com/zsxsoft](https://github.com/zsxsoft)
- [https://api.github.com/users/zsxsoft/gists%7B/gist_id%7D](https://api.github.com/users/zsxsoft/gists%7B/gist_id%7D)
- [https://api.github.com/users/zsxsoft/repos](https://api.github.com/users/zsxsoft/repos)
- [https://avatars.githubusercontent.com/u/2398785?v=4](https://avatars.githubusercontent.com/u/2398785?v=4)
- [https://api.github.com/users/zsxsoft/events%7B/privacy%7D](https://api.github.com/users/zsxsoft/events%7B/privacy%7D)

## Related threats

- [Mermaid radar diagrams denial of service via unchecked ticks input](https://junglewise.ai/threats/cve-2026-71439-mermaid-radar-diagrams-denial-of-service-via-unchecked-ticks)
- [Mermaid prototype pollution in configuration APIs](https://junglewise.ai/threats/cve-2026-71438-mermaid-prototype-pollution-in-configuration-apis)
- [Mermaid prototype pollution in architecture-beta diagrams](https://junglewise.ai/threats/cve-2026-71437-mermaid-prototype-pollution-in-architecture-beta-diagrams)
- [Mermaid infinite loop in XY Charts axis processing](https://junglewise.ai/threats/cve-2026-71436-mermaid-infinite-loop-in-xy-charts-axis-processing)
- [Mermaid CSS injection via sibling combinators](https://junglewise.ai/threats/cve-2026-50159-mermaid-css-injection-via-sibling-combinators)