Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection — CVE-2026-41149

Summary

### Impact Under the default configuration, Mermaid state diagram's `classDef` allow DOM injection that escapes the SVG, although `<script>` tags are removed, preventing XSS. #### Proof-of-concept ``` stateDiagram-v2 classDef xss fill:red</style></svg><style>*{x:x;y:y;overflow:visible!important;contain:none!important;transform:none!important;filter:none!important;clip-path:none!important}</style><div…

Product

npm: mermaid

What to do

General, cautious steps (verify details in the official source):

• Review exposure and plan remediation based on risk and environment.
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Related advisories