CVE-2025-54881 – mermaid

Package

Manager: npm
Name: mermaid
Vulnerable Version: >=11.0.0-alpha.1 <11.10.0 || >=10.9.0-rc.1 <10.9.4

Severity

Level: Medium

CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N/E:U/RL:O/RC:C

CVSS v4.0: 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

EPSS: 0.00059 pctl0.18453

Details

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: ```ts 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](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.0). ### 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! ``` Here is a PoC on mermaid.live: https://mermaid.live/edit#pako:eNpVUMtOwzAQ_BWzyoFKaRTyaFILiio4IK7ckA-1km1iKbaLY6spUf4dJ0AF68uOZ2dm7REqXSNQ6PHDoarwWfDGcMkUudaJGysqceLKkj3hPdl3osJ7IRvSm-qBwcCAaIXGaONRrSsnUdnobITF28PQ954lwXglai25UNNhxWAXBMyXxcGOi-3kL_5k79e73atuFSUv2HWazH1IWn0m3CC5aPf4b3p2WK--BW-4DJCOWzQ3TM0HQmiMqIFa4zAEicZv4iGMsw0D26JEBtS3NR656ywDpiYv869_11r-Ko12TQv0yLveI3eqfcjP111HUNVonrRTFuhdsVgAHWEAmuRxlG7SuEzKMi-yJAnhAjTLIk_EcbFJtuk2y9MphM8lM47KIp--AOZghtU ### 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`.

Metadata

Created: 2025-08-19T20:16:58Z
Modified: 2025-08-22T22:52:04Z
Source: https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/08/GHSA-7rqq-prvp-x9jh/GHSA-7rqq-prvp-x9jh.json
CWE IDs: ["CWE-79"]
Alternative ID: GHSA-7rqq-prvp-x9jh
Finding: F008
Auto approve: 1