GHSA-87f9-hvmw-gh4p

Source

https://github.com/advisories/GHSA-87f9-hvmw-gh4p

Import Source

https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-87f9-hvmw-gh4p/GHSA-87f9-hvmw-gh4p.json

JSON Data

https://api.osv.dev/v1/vulns/GHSA-87f9-hvmw-gh4p

Aliases

CVE-2026-41159

Published

2026-05-11T19:37:00Z

Modified

2026-05-11T19:49:39.861570Z

Severity

5.3 (Medium) CVSS_V4 - 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 CVSS Calculator

Summary

Mermaid: Improper sanitization of configuration leads to CSS injection

Details

Impact

Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options.

Live demo: mermaid.live

Example code:

%%{init: {"fontFamily": "x;a{b} :not(&){background:green !important} c{d}"}}%%
flowchart LR
    A --> B

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.

Patches

Workarounds

If you can't upgrade mermaid, you can set the secure config value in the mermaid config to avoid allowing diagrams to modify fontFamily, themeCSS, altFontFamily, and themeVariables.

Setting "securityLevel": "sandbox" will also prevent this.

Credits

Reported by @zsxsoft on behalf of @KeenSecurityLab

Database specific

{
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-11T19:37:00Z",
    "cwe_ids": [
        "CWE-94"
    ],
    "severity": "MODERATE",
    "nvd_published_at": null
}

References

Affected packages

npm / mermaid

Package

Name: mermaid; View open source insights on deps.dev
Purl: pkg:npm/mermaid

Affected ranges

Type: SEMVER
Events: Introduced

11.0.0-alpha.1

Fixed

11.15.0

Database specific

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-87f9-hvmw-gh4p/GHSA-87f9-hvmw-gh4p.json"

last_known_affected_version_range

"<= 11.14.0"