{
"id": "GHSA-87f9-hvmw-gh4p",
"aliases": [
"CVE-2026-41159"
],
"details": "### Impact\n\nMermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the `fontFamily`, `themeCSS`, and `altFontFamily` configuration options.\n\nLive demo: [mermaid.live](https://mermaid.live/edit#pako:eNpNjktLxDAUhf9KvFBR6JS-60QQfODKlUvJ5k6TtsEmKTHFGUP-u-mI6Nmdy3fOPR56wwVQSBIvtXSUeAaD0e4ZlZxPDChhcLxFfwiEauOuLq_9Afv30ZpVczpaITS5kGox1qF2gfSeBwYhJAnThAyz-ewntI68vG5-0z3Z7e7IA9OQwmglB-rsKlJQwircLPgNZeAmocTPAi4GXGfHgOkQYwvqN2PUbzJuGSegA84f0a0LRyeeJI4W_xChubCPcbQD2pwbgHo4Aq2aKmvbqq3zoiu7pizqFE6RybN9VFfFY1HWXRVS-Dr_zLObrt7_V_gGGXZlGg)\n\nExample code:\n\n```\n%%{init: {\"fontFamily\": \"x;a{b} :not(&){background:green !important} c{d}\"}}%%\nflowchart LR\n A --> B\n```\n\nThe 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.\n\nThis allows page defacement and DOM attribute exfiltration via CSS `:has()` selectors.\n\n### Patches\n\n- [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [64769738d5b59211e1decb471ffbaca8afec51aa](https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa))\n- [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [a9d9f0d8eb790349121508688cd338253fd80d76](https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76))\n\n### Workarounds\n\nIf you can't upgrade mermaid, you can set the [`secure`](https://mermaid.js.org/config/schema-docs/config.html#secure) config value in the mermaid config to avoid allowing diagrams to modify `fontFamily`, `themeCSS`, `altFontFamily`, and `themeVariables`.\n\nSetting [`\"securityLevel\": \"sandbox\"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will also prevent this.\n\n### Credits\n\nReported by @zsxsoft on behalf of @KeenSecurityLab",
"summary": "Mermaid: Improper sanitization of configuration leads to CSS injection",
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "11.0.0-alpha.1"
},
{
"fixed": "11.15.0"
}
]
}
],
"package": {
"name": "mermaid",
"ecosystem": "npm"
},
"database_specific": {
"last_known_affected_version_range": "<= 11.14.0"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "10.9.6"
}
]
}
],
"package": {
"name": "mermaid",
"ecosystem": "npm"
},
"database_specific": {
"last_known_affected_version_range": "<= 10.9.5"
}
}
],
"modified": "2026-07-01T19:21:33Z",
"severity": [
{
"type": "CVSS_V4",
"score": "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"
}
],
"published": "2026-05-11T19:37:00Z",
"references": [
{
"url": "https://github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvmw-gh4p",
"type": "WEB"
},
{
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41159",
"type": "ADVISORY"
},
{
"url": "https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa",
"type": "WEB"
},
{
"url": "https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76",
"type": "WEB"
},
{
"url": "https://github.com/mermaid-js/mermaid",
"type": "PACKAGE"
},
{
"url": "https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0",
"type": "WEB"
},
{
"url": "https://github.com/mermaid-js/mermaid/releases/tag/[email protected] ",
"type": "WEB"
},
{
"url": "https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6",
"type": "WEB"
}
],
"schema_version": "1.4.0",
"database_specific": {
"cwe_ids": [
"CWE-94"
],
"severity": "MODERATE",
"github_reviewed": true,
"nvd_published_at": "2026-05-29T15:16:22Z",
"github_reviewed_at": "2026-05-11T19:37:00Z"
}
}