EUVD-2026-31520Published

Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection

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cve-program · CVE-2026-41149

Published

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Versions 10.9.5 and earlier, as well as 11.0.0-alpha.1 through 11.14.0, are vulnerable to HTML injection under the default configuration. Specifically, the classDef directive in Mermaid state diagrams permits DOM injection that escapes the SVG context. However, <script> tags are stripped, which prevents cross-site scripting (XSS). This issue has been fixed in versions 10.9.6 and 11.15.0. If developers are unable to immediately upgrade, they can work around this issue by setting "securityLevel": "sandbox", which prevents the issue by rendering the mermaid diagram in a sandboxed <iframe>.

Source published: 22 May 2026 22:34:36 UTC
Source modified: 23 May 2026 03:22:44 UTC
Saved here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

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CVSS 4.0 · 5.3 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

euvd · EUVD-2026-31520

Published

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datePublished: May 22, 2026, 10:34:36 PM

dateUpdated: May 23, 2026, 3:22:44 AM

Source published: May 22, 2026, 10:34:36 PM (timezone not stated)
Source modified: May 23, 2026, 3:22:44 AM (timezone not stated)
Saved here: 15 Nov 2026 12:03:07 UTC
Source terms: ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 5.3 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

nvd · CVE-2026-41149

Published

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Source analysis status: Deferred

Weakness classifications: CWE-94

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published: 2026-05-22T23:16:53.750

lastModified: 2026-07-23T11:10:00.120

Source published: 22 May 2026 23:16:53 UTC
Source modified: 23 Jul 2026 11:10:00 UTC
Saved here: 25 Oct 2026 09:17:30 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

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CVSS 4.0 · [email protected] · Secondary · 5.3 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

osv · GHSA-ghcm-xqfw-q4vr

Published

### 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:::xss ``` ### Patches - [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [37ff937f1da2e19f882fd1db01235db4d01f4056](https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056)) - [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3](https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3)) ### Workarounds If you can not update to a patched version, setting [`"securityLevel": "sandbox"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will prevent this, by rendering the mermaid diagram in a sandboxed `<iframe>`. ### Credits Thanks to @zsxsoft from @KeenSecurityLab for reporting this vulnerability.

Source published: 11 May 2026 19:36:46 UTC
Source modified: 10 Sep 2026 03:51:05 UTC
Saved here: 24 Oct 2026 13:17:17 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · 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

Publisher rating · MODERATE