Mermaid improperly sanitizes sequence diagram labels leading to XSS
Summary
In the default configuration of mermaid 11.9.0, user supplied input for sequence diagram labels is passed to innerHTML during calculation of element size, causing XSS.
Details
Sequence diagram node labels with KaTeX delimiters are passed through calculateMathMLDimensions. This method passes the full label to innerHTML which allows allows malicious users to inject arbitrary HTML and cause XSS when mermaid-js is used in it's default configuration (with KaTeX support enabled).
The vulnerability lies here:
export const calculateMathMLDimensions = async (text: string, config: MermaidConfig) => {
text = await renderKatex(text, config);
const divElem = document.createElement('div');
divElem.innerHTML = text; // XSS sink, text has not been sanitized.
divElem.id = 'katex-temp';
divElem.style.visibility = 'hidden';
divElem.style.position = 'absolute';
divElem.style.top = '0';
const body = document.querySelector('body');
body?.insertAdjacentElement('beforeend', divElem);
const dim = { width: divElem.clientWidth, height: divElem.clientHeight };
divElem.remove();
return dim;
};The calculateMathMLDimensions method was introduced in 5c69e5fdb004a6d0a2abe97e23d26e223a059832 two years ago, which was released in Mermaid 10.9.0.
PoC
Render the following diagram and observe the modified DOM.
sequenceDiagram
participant A as Alice<img src="x" onerror="document.write(`xss on ${document.domain}`)">$$\\text{Alice}$$
A->>John: Hello John, how are you?
Alice-)John: See you later!Impact
XSS on all sites that use mermaid and render user supplied diagrams without further sanitization.
Remediation
The value of the text argument for the calculateMathMLDimensions method needs to be sanitized before getting passed on to innerHTML.
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Paquete de npm | mermaid | >= 11.0.0-alpha.1, < 11.10.0, >= 10.9.0-rc.1, < 10.9.4 | 11.10.0, 10.9.4 |
Referencias
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh
- https://nvd.nist.gov/vuln/detail/CVE-2025-54881
- https://github.com/mermaid-js/mermaid/commit/5c69e5fdb004a6d0a2abe97e23d26e223a059832
- https://github.com/mermaid-js/mermaid/commit/685516a85ec1df64cefd4fd15f26533be87d458e
- https://github.com/mermaid-js/mermaid
- Vector CVSS
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N- Debilidad (CWE)
CWE-79- Plataforma
- npm
- Paquete
mermaid- Publicada
- 19.08.2025
- Actualizado
- 11.10.2026 10:22
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-7rqq-prvp-x9jh - 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 improperly sanitizes sequence diagram labels leading to XSS esta entrada
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