Vulnerability · Published May 29, 2026 · Assigned by GitHub_M

CVE-2026-41159Mermaid: Improper sanitization of configuration leads to CSS injection

Medium 5.3

In plain English

A medium-severity code injection in mermaid from mermaid-js. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 42% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.3Medium

Exploit odds (30 days)0.5%top 57.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	node-mermaid	no fix listed	DEBIAN-CVE-2026-41159
Ubuntu:22.04:LTS	node-mermaid	no fix listed	UBUNTU-CVE-2026-41159
Ubuntu:26.10	node-mermaid	no fix listed	UBUNTU-CVE-2026-41159
npm	mermaid	11.15.0	GHSA-87f9-hvmw-gh4p
npm	mermaid	10.9.6	GHSA-87f9-hvmw-gh4p

Affected products (as reported)

Vendor	Product	Versions
mermaid-js	mermaid	>= 11.0.0-alpha.1, < 11.15.0< 10.9.6

Weakness: CWE-94 · Vector: 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

References

https://github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvmw-gh4p x_refsource_CONFIRM
https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa x_refsource_MISC
https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76 x_refsource_MISC
https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.15.0 x_refsource_MISC
https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6 x_refsource_MISC