Description
Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options. The 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. This allows page defacement and DOM attribute exfiltration via CSS :has() selectors. This vulnerability is fixed in 10.9.6 and 11.15.0.
Affected products
mermaid_project: mermaid
References5
- github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471f…
- github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688c…
- github.com/mermaid-js/mermaid/releases/tag/[email protected] Release Notes
- github.com/mermaid-js/mermaid/releases/tag/v10.9.6 Release Notes
- github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvm… Third Party Advisory
Metrics
- CVSS 3.1
-
5.3
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - CVSS 4.0
-
5.3
MEDIUM
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 42 · as of 15 November 2026
- CWE
- CWE-94
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