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CVE-2026-41159

Mermaid: Improper sanitization of configuration leads to CSS injection

MEDIUM
5.3
CVSS Score
Published: May 29, 2026 at 01:53 PM UTC
Updated: July 21, 2026 at 01:39 PM UTC
2 products affected across 2 vendorsMermaidMermaid

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.5%
SSVC
No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mermaid· Mermaid Projectnpm
95%
v < 10.9.611.0.0 ≤ v < 11.15.0
Affected range stops below 10.9.6, so it looks safe — our inference, not a vendor statement
Affected range stops below 11.15.0, so it looks safe — our inference, not a vendor statement
Mermaid· Mermaid Js
60%
v < 10.9.6v < 11.15.0
Affected range stops below 10.9.6, so it looks safe — our inference, not a vendor statement
Affected range stops below 11.15.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (6)

x_refsource_CONFIRMThird Party Advisory
Source: cverecord
https://github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvmw-gh4p
Source: cverecord
https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aahttps://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76
x_refsource_MISCRelease Notes
Source: cverecord
https://github.com/mermaid-js/mermaid/releases/tag/[email protected]
x_refsource_MISCRelease Notes
Source: cverecord
https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6
x_refsource_MISC
Source: cverecord
https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa
x_refsource_MISC
Source: cverecord
https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMGitHub_M
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-94

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