GHSA-7rqq-prvp-x9jh Mermaid improperly sanitizes sequence diagram labels leading to XSS

• npm mermaid: >= 11.0.0-alpha.1, < 11.10.0 → fixed in 11.10.0 • npm mermaid: >= 10.9.0-rc.1, < 10.9.4 → fixed in 10.9.4

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. PoC Render the following diagram and observe the modified DOM. ``` sequenceDiagram participant A as Alice$$\\text{Alice}$$ 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`.