PT-2026-39888 · Npm · Mermaid

Published 2026-05-11 · Updated 2026-05-12 · CVE-2026-41159

Positive Technologies (AI Summary)

CVSS v4.0

5.3

Medium

Base vector

AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L

Name of the Vulnerable Software and Affected Versions Mermaid versions prior to 11.15.0 Mermaid versions prior to 10.9.6

Description Default configuration allows the injection of CSS that applies outside of the Mermaid diagram. This occurs through the fontFamily, themeCSS, and altFontFamily configuration options, exploiting how stylis handles scope references. Specifically, using :not(&) escapes automatic scoping, allowing styles to be applied to all page elements. Additionally, global at-rules such as @font-face, @keyframes, and @counter-style can be injected as they are hoisted to the top level. This can lead to page defacement and the exfiltration of DOM attributes using CSS :has() selectors.

Recommendations Update to version 11.15.0 or later. Update to version 10.9.6 or later. Set the secure configuration value to avoid allowing diagrams to modify fontFamily, themeCSS, altFontFamily, and themeVariables. Set securityLevel to sandbox to prevent the issue.

Fix

Code Injection

Weakness Enumeration

CWE-94

Related Identifiers

CVE-2026-41159

GHSA-87F9-HVMW-GH4P

Affected Products

Mermaid

References · 8

• https://osv.dev/vulnerability/GHSA-87f9-hvmw-gh4p · Vendor Advisory
• https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa · Note
• https://github.com/mermaid-js/mermaid · Note
• https://github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvmw-gh4p · Note
• https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6 · Note
• https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76 · Note
• https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0 · Note
• https://twitter.com/dailycve/status/2053990060324737163 · Twitter Post