CVE-2026-41159: Mermaid Improper Sanitization Of Configuration Leads Vulnerability

Q: What is CVE-2026-41159?

CVE-2026-41159 is a security vulnerability in Mermaid involving Improper sanitization of configuration leads to CSS injection under CWE-94: Improper Control of Generation of Code ('Code Injection').

Q: Which Mermaid versions are affected?

Affected versions include releases prior to 11.15.0, 10.9.6 across affected packages: mermaid.

Q: What version fixes CVE-2026-41159?

Upgrading to 11.15.0, 10.9.6 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is mermaid affected?

Yes, mermaid is affected in releases prior to 11.15.0, 10.9.6. Upgrade your dependency to 11.15.0, 10.9.6 or later.

Q: What CWE is associated with CVE-2026-41159?

CVE-2026-41159 is classified under CWE-94: Improper Control of Generation of Code ('Code Injection') (The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.).

Q: How can I check npm dependencies for CVE-2026-41159?

Run the dependency tree command: 'npm ls mermaid'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

MODERATE

Advisory Identifier: GHSA-87f9-hvmw-gh4p

CWE-94

Published 2026-05-11

Advisory Summary

CVE-2026-41159 is a MODERATE improper sanitization of configuration leads vulnerability (CWE-94: Improper Control of Generation of Code ('Code Injection')) affecting Mermaid libraries in the npm ecosystem. The issue involves improper sanitization of configuration leads to css injection. Remediation is available by upgrading affected packages to version 11.15.0, 10.9.6.

CVE-2026-41159 at a Glance

CVE Identifier CVE-2026-41159

GHSA Identifier GHSA-87f9-hvmw-gh4p

Severity MODERATE

CVSS v3.1 Base Score N/A

CWE Classification CWE-94: Improper Control of Generation of Code ('Code Injection')

Affected Product Mermaid

Package Ecosystem npm

Published Date 2026-05-11

Last Updated 2026-07-01

How to Fix CVE-2026-41159

To remediate this vulnerability, upgrade all affected Mermaid dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

mermaid fixed: 11.15.0

npm install mermaid@11.15.0

mermaid fixed: 10.9.6

npm install mermaid@10.9.6

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

npm ls mermaid

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-41159, inspect your project dependencies using npm:

npm ls mermaid

Analyze the terminal output to locate any version of Mermaid in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 11.15.0), your application is affected.

Note: The npm ls mermaid command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-94: Improper Control of Generation of Code ('Code Injection'), where the product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. In Mermaid, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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](https://mermaid.live/edit#pako:eNpNjktLxDAUhf9KvFBR6JS-60QQfODKlUvJ5k6TtsEmKTHFGUP-u-mI6Nmdy3fOPR56wwVQSBIvtXSUeAaD0e4ZlZxPDChhcLxFfwiEauOuLq_9Afv30ZpVczpaITS5kGox1qF2gfSeBwYhJAnThAyz-ewntI68vG5-0z3Z7e7IA9OQwmglB-rsKlJQwircLPgNZeAmocTPAi4GXGfHgOkQYwvqN2PUbzJuGSegA84f0a0LRyeeJI4W_xChubCPcbQD2pwbgHo4Aq2aKmvbqq3zoiu7pizqFE6RybN9VFfFY1HWXRVS-Dr_zLObrt7_V_gGGXZlGg) 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 - [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [64769738d5b59211e1decb471ffbaca8afec51aa](https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa)) - [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [a9d9f0d8eb790349121508688cd338253fd80d76](https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76)) ### Workarounds If you can't upgrade mermaid, you can set the [`secure`](https://mermaid.js.org/config/schema-docs/config.html#secure) config value in the mermaid config to avoid allowing diagrams to modify `fontFamily`, `themeCSS`, `altFontFamily`, and `themeVariables`. Setting [`"securityLevel": "sandbox"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will also prevent this. ### Credits Reported by @zsxsoft on behalf of @KeenSecurityLab

CVE-2026-41159 Affected Mermaid Versions

2 component(s)

Fixed Versions:

11.15.010.9.6

Product / Package	Ecosystem	Affected Versions	Fixed Version
mermaid npm/mermaid	npm	≥ 11.0.0-alpha.1 < 11.15.0	11.15.0
mermaid npm/mermaid	npm	< 10.9.6	10.9.6

References

GitHub Advisory / Wiki ADVISORY

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

NVD — CVE-2026-41159 NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-41159

Security Fix Commit FIX COMMIT

https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa

Security Fix Commit FIX COMMIT

https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76

Mermaid Source Repository REPOSITORY

https://github.com/mermaid-js/mermaid

Mermaid Release RELEASE

https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0

Mermaid Release RELEASE

https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.15.0

Mermaid Release RELEASE

https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6

Frequently Asked Questions

What is CVE-2026-41159?

CVE-2026-41159 is a security vulnerability in Mermaid involving Improper sanitization of configuration leads to CSS injection under CWE-94: Improper Control of Generation of Code ('Code Injection').

Which Mermaid versions are affected?

Affected versions include releases prior to 11.15.0, 10.9.6 across affected packages: mermaid.

What version fixes CVE-2026-41159?

Upgrading to 11.15.0, 10.9.6 (or the latest patched release for your respective branch) resolves the vulnerability.

Is mermaid affected?

Yes, mermaid is affected in releases prior to 11.15.0, 10.9.6. Upgrade your dependency to 11.15.0, 10.9.6 or later.

What CWE is associated with CVE-2026-41159?

CVE-2026-41159 is classified under CWE-94: Improper Control of Generation of Code ('Code Injection') (The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.).

How can I check npm dependencies for CVE-2026-41159?

Run the dependency tree command: 'npm ls mermaid'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

Machine-readable OSV JSON OSV v1.5 Schema

Normalized schema output

View Raw JSON

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-87f9-hvmw-gh4p",
  "modified" : "2026-07-01T19:21:33Z",
  "published" : "2026-05-11T19:37:00Z",
  "aliases" : [ "CVE-2026-41159" ],
  "summary" : "Mermaid: Improper sanitization of configuration leads to CSS injection",
  "details" : "### Impact\n\nMermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the `fontFamily`, `themeCSS`, and `altFontFamily` configuration options.\n\nLive demo: [mermaid.live](https://mermaid.live/edit#pako:eNpNjktLxDAUhf9KvFBR6JS-60QQfODKlUvJ5k6TtsEmKTHFGUP-u-mI6Nmdy3fOPR56wwVQSBIvtXSUeAaD0e4ZlZxPDChhcLxFfwiEauOuLq_9Afv30ZpVczpaITS5kGox1qF2gfSeBwYhJAnThAyz-ewntI68vG5-0z3Z7e7IA9OQwmglB-rsKlJQwircLPgNZeAmocTPAi4GXGfHgOkQYwvqN2PUbzJuGSegA84f0a0LRyeeJI4W_xChubCPcbQD2pwbgHo4Aq2aKmvbqq3zoiu7pizqFE6RybN9VFfFY1HWXRVS-Dr_zLObrt7_V_gGGXZlGg)\n\nExample code:\n\n```\n%%{init: {\"fontFamily\": \"x;a{b} :not(&){background:green !important} c{d}\"}}%%\nflowchart LR\n    A --> B\n```\n\nThe 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.\n\nThis allows page defacement and DOM attribute exfiltration via CSS `:has()` selectors.\n\n### Patches\n\n- [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [64769738d5b59211e1decb471ffbaca8afec51aa](https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa))\n- [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [a9d9f0d8eb790349121508688cd338253fd80d76](https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76))\n\n### Workarounds\n\nIf you can't upgrade mermaid, you can set the [`secure`](https://mermaid.js.org/config/schema-docs/config.html#secure) config value in the mermaid config to avoid allowing diagrams to modify `fontFamily`, `themeCSS`, `altFontFamily`, and `themeVariables`.\n\nSetting [`\"securityLevel\": \"sandbox\"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel)  will also prevent this.\n\n### Credits\n\nReported by @zsxsoft on behalf of @KeenSecurityLab",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "mermaid"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.0.0-alpha.1"
      }, {
        "fixed" : "11.15.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 11.14.0"
    }
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "mermaid"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "10.9.6"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 10.9.5"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/security/advisories/GHSA-87f9-hvmw-gh4p"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41159"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/commit/64769738d5b59211e1decb471ffbaca8afec51aa"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/commit/a9d9f0d8eb790349121508688cd338253fd80d76"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mermaid-js/mermaid"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.15.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-94" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T19:37:00Z",
    "nvd_published_at" : "2026-05-29T15:16:22Z"
  }
}

CVSS V4

N/A MODERATE

Attack Vector N/A

Attack Complexity N/A

Privileges Required N/A

User Interaction N/A

Scope N/A

Confidentiality N/A

Integrity N/A

Availability N/A

Vector String

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

Advisory Metadata

Source ID: GHSA-87f9-hvmw-gh4p
Schema Version: 1.4.0
Published: 2026-05-11 19:37
Last Modified: 2026-07-01 19:21
Database Record File: advisories/github-reviewed/2026/05/GHSA-87f9-hvmw-gh4p/GHSA-87f9-hvmw-gh4p.json