Mermaid: Improper sanitization of configuration leads to CSS injection
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
Example code:
%%{init: {"fontFamily": "x;a{b} :not(&){background:green !important} c{d}"}}%%
flowchart LR
A --> BThe 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 (see 64769738d5b59211e1decb471ffbaca8afec51aa)
- v10.9.6 (see a9d9f0d8eb790349121508688cd338253fd80d76)
Workarounds
If you can't upgrade mermaid, you can set the secure config value in the mermaid config to avoid allowing diagrams to modify fontFamily, themeCSS, altFontFamily, and themeVariables.
Setting "securityLevel": "sandbox" will also prevent this.
Credits
Reported by @zsxsoft on behalf of @KeenSecurityLab
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Paquete de npm | mermaid | >= 11.0.0-alpha.1, < 11.15.0, < 10.9.6 | 11.15.0, 10.9.6 |
Referencias
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvmw-gh4p
- https://nvd.nist.gov/vuln/detail/CVE-2026-41159
- https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa
- https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76
- 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/mermaid@11.15.0
- https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6
- Vector CVSS
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- Debilidad (CWE)
CWE-94- Plataforma
- npm
- Paquete
mermaid- Publicada
- 11.05.2026
- Actualizado
- 11.10.2026 10:22
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-87f9-hvmw-gh4p - CC BY 4.0
Historial de vulnerabilidades: mermaid
Todas las vulnerabilidades publicadas de este paquete (Paquete de npm), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 16
- Primera → última
- 09.2020 08.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Alta 3
- Media 12
- Baja 1
Divulgaciones por año
- 2020: 1
- 2021: 1
- 2022: 2
- 2023: 0
- 2024: 1
- 2025: 2
- 2026: 9
-
Mermaid: Improper sanitization of configuration leads to CSS injection esta entrada
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