{"id":"GHSA-7rqq-prvp-x9jh","summary":"Mermaid improperly sanitizes sequence diagram labels leading to XSS","details":"### Summary\nIn 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.\n\n### Details\nSequence 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). \n\nThe vulnerability lies here:\n\n```ts\nexport const calculateMathMLDimensions = async (text: string, config: MermaidConfig) =\u003e {\n  text = await renderKatex(text, config);\n  const divElem = document.createElement('div');\n  divElem.innerHTML = text; // XSS sink, text has not been sanitized.\n  divElem.id = 'katex-temp';\n  divElem.style.visibility = 'hidden';\n  divElem.style.position = 'absolute';\n  divElem.style.top = '0';\n  const body = document.querySelector('body');\n  body?.insertAdjacentElement('beforeend', divElem);\n  const dim = { width: divElem.clientWidth, height: divElem.clientHeight };\n  divElem.remove();\n  return dim;\n};\n```\n\nThe `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).\n\n### PoC\nRender the following diagram and observe the modified DOM.\n\n```\nsequenceDiagram\n    participant A as Alice\u003cimg src=\"x\" onerror=\"document.write(`xss on ${document.domain}`)\"\u003e$$\\\\text{Alice}$$\n    A-\u003e\u003eJohn: Hello John, how are you?\n    Alice-)John: See you later!\n```\n\nHere is a PoC on mermaid.live: https://mermaid.live/edit#pako:eNpVUMtOwzAQ_BWzyoFKaRTyaFILiio4IK7ckA-1km1iKbaLY6spUf4dJ0AF68uOZ2dm7REqXSNQ6PHDoarwWfDGcMkUudaJGysqceLKkj3hPdl3osJ7IRvSm-qBwcCAaIXGaONRrSsnUdnobITF28PQ954lwXglai25UNNhxWAXBMyXxcGOi-3kL_5k79e73atuFSUv2HWazH1IWn0m3CC5aPf4b3p2WK--BW-4DJCOWzQ3TM0HQmiMqIFa4zAEicZv4iGMsw0D26JEBtS3NR656ywDpiYv869_11r-Ko12TQv0yLveI3eqfcjP111HUNVonrRTFuhdsVgAHWEAmuRxlG7SuEzKMi-yJAnhAjTLIk_EcbFJtuk2y9MphM8lM47KIp--AOZghtU\n\n### Impact\nXSS on all sites that use mermaid and render user supplied diagrams without further sanitization.\n\n### Remediation\nThe value of the `text` argument for the `calculateMathMLDimensions` method needs to be sanitized before getting passed on to `innerHTML`.","aliases":["CVE-2025-54881"],"modified":"2026-08-07T08:12:11.518764754Z","published":"2025-08-19T20:16:58Z","database_specific":{"nvd_published_at":"2025-08-19T17:15:41Z","cwe_ids":["CWE-79"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2025-08-19T20:16:58Z"},"references":[{"type":"WEB","url":"https://github.com/mermaid-js/mermaid/security/advisories/GHSA-7rqq-prvp-x9jh"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-54881"},{"type":"WEB","url":"https://github.com/mermaid-js/mermaid/commit/5c69e5fdb004a6d0a2abe97e23d26e223a059832"},{"type":"WEB","url":"https://github.com/mermaid-js/mermaid/commit/685516a85ec1df64cefd4fd15f26533be87d458e"},{"type":"PACKAGE","url":"https://github.com/mermaid-js/mermaid"}],"affected":[{"package":{"name":"mermaid","ecosystem":"npm","purl":"pkg:npm/mermaid"},"ranges":[{"type":"SEMVER","events":[{"introduced":"11.0.0-alpha.1"},{"fixed":"11.10.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/08/GHSA-7rqq-prvp-x9jh/GHSA-7rqq-prvp-x9jh.json"}},{"package":{"name":"mermaid","ecosystem":"npm","purl":"pkg:npm/mermaid"},"ranges":[{"type":"SEMVER","events":[{"introduced":"10.9.0-rc.1"},{"fixed":"10.9.4"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/08/GHSA-7rqq-prvp-x9jh/GHSA-7rqq-prvp-x9jh.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}