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Mermaid: Improper sanitization of configuration leads to CSS injection

CVSS 4.0 5.3 MEDIUMEUVD CVSS 4.0 5.3 CVSS 4.0 · [email protected] · Secondary 5.3 MEDIUMCVSS 3.1 · [email protected] · Primary 5.3 MEDIUMCVSS_V4 Publisher rating MODERATEFixed by mermaid 11.15.0Fixed by mermaid 10.9.6KEV status unknown

cve-program · CVE-2026-41159

Published

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options. The injected CSS exploits stylis's & (scope reference) handling. :not(&) escapes the #mermaid-xxx automatic scoping, applying styles to all page elements. Global at-rules (@font-face, @keyframes, @counter-style) are also injectable as stylis hoists them to top level. This allows page defacement and DOM attribute exfiltration via CSS :has() selectors. This vulnerability is fixed in 10.9.6 and 11.15.0.

Read the publisher's advisory

euvd · EUVD-2026-33324

Published

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options. The injected CSS exploits stylis's & (scope reference) handling. :not(&) escapes the #mermaid-xxx automatic scoping, applying styles to all page elements. Global at-rules (@font-face, @keyframes, @counter-style) are also injectable as stylis hoists them to top level. This allows page defacement and DOM attribute exfiltration via CSS :has() selectors. This vulnerability is fixed in 10.9.6 and 11.15.0.

Read the publisher's advisory

nvd · CVE-2026-41159

Published

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options. The injected CSS exploits stylis's & (scope reference) handling. :not(&) escapes the #mermaid-xxx automatic scoping, applying styles to all page elements. Global at-rules (@font-face, @keyframes, @counter-style) are also injectable as stylis hoists them to top level. This allows page defacement and DOM attribute exfiltration via CSS :has() selectors. This vulnerability is fixed in 10.9.6 and 11.15.0.

Read the publisher's advisory

osv · GHSA-87f9-hvmw-gh4p

Published

### Impact Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the `fontFamily`, `themeCSS`, and `altFontFamily` configuration options. Live demo: [mermaid.live](https://mermaid.live/edit#pako:eNpNjktLxDAUhf9KvFBR6JS-60QQfODKlUvJ5k6TtsEmKTHFGUP-u-mI6Nmdy3fOPR56wwVQSBIvtXSUeAaD0e4ZlZxPDChhcLxFfwiEauOuLq_9Afv30ZpVczpaITS5kGox1qF2gfSeBwYhJAnThAyz-ewntI68vG5-0z3Z7e7IA9OQwmglB-rsKlJQwircLPgNZeAmocTPAi4GXGfHgOkQYwvqN2PUbzJuGSegA84f0a0LRyeeJI4W_xChubCPcbQD2pwbgHo4Aq2aKmvbqq3zoiu7pizqFE6RybN9VFfFY1HWXRVS-Dr_zLObrt7_V_gGGXZlGg) Example code: ``` %%{init: {"fontFamily": "x;a{b} :not(&){background:green !important} c{d}"}}%% flowchart LR A --> B ``` The injected CSS exploits stylis's `&` (scope reference) handling. `:not(&)` escapes the `#mermaid-xxx` automatic scoping, applying styles to all page elements. Global at-rules (`@font-face`, `@keyframes`, `@counter-style`) are also injectable as stylis hoists them to top level. This allows page defacement and DOM attribute exfiltration via CSS `:has()` selectors. ### Patches - [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [64769738d5b59211e1decb471ffbaca8afec51aa](https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa)) - [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [a9d9f0d8eb790349121508688cd338253fd80d76](https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76)) ### Workarounds If you can't upgrade mermaid, you can set the [`secure`](https://mermaid.js.org/config/schema-docs/config.html#secure) config value in the mermaid config to avoid allowing diagrams to modify `fontFamily`, `themeCSS`, `altFontFamily`, and `themeVariables`. Setting [`"securityLevel": "sandbox"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will also prevent this. ### Credits Reported by @zsxsoft on behalf of @KeenSecurityLab

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15 Nov 2026 12:03:09 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

13 Nov 2026 11:58:00 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

11 Nov 2026 10:58:38 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

9 Nov 2026 10:05:37 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

7 Nov 2026 09:27:56 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

5 Nov 2026 08:55:16 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

3 Nov 2026 07:59:51 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

1 Nov 2026 07:05:48 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

30 Oct 2026 06:49:53 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

28 Oct 2026 05:06:55 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

euvd · EUVD-2026-33324 · Published

25 Oct 2026 09:17:30 UTC

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the f…

nvd · CVE-2026-41159 · Published

24 Oct 2026 13:17:17 UTC

Mermaid: Improper sanitization of configuration leads to CSS injection

osv · GHSA-87f9-hvmw-gh4p · Published

23 Oct 2026 15:48:27 UTC

Mermaid: Improper sanitization of configuration leads to CSS injection

cve-program · CVE-2026-41159 · Published

ChangeIntel

An IT change radar: releases, security, known issues, retirements, documentation changes, and service status from public sources. Every item links to supporting evidence; dates and statuses can change after they are read.

Sources read 15 Nov 12:11 UTC · 256 of 275 readable · 252 fully read · documentation 469/469 current