CVE-2026-41159
Mermaid: Improper sanitization of configuration leads to CSS injection
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.
How to fix CVE-2026-41159
To remediate CVE-2026-41159, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 11.15.0 or later
Is CVE-2026-41159 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0
- >= 11.0.0-alpha.1, < 11.15.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | 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 |
| osv | CVSS 3.1 | MEDIUM5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |