CVE-2026-41149: Mermaid Improper Sanitization Of `classDef` Vulnerability

MODERATE
Advisory Identifier: GHSA-ghcm-xqfw-q4vr
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CWE-94
Published
Advisory Summary

CVE-2026-41149 is a MODERATE improper sanitization of `classdef` vulnerability (CWE-94: Improper Control of Generation of Code ('Code Injection')) affecting Mermaid libraries in the npm ecosystem. The issue involves improper sanitization of `classdef` in state diagrams leads to html injection. Remediation is available by upgrading affected packages to version 11.15.0, 10.9.6.

CVE-2026-41149 at a Glance

CVE Identifier CVE-2026-41149
GHSA Identifier GHSA-ghcm-xqfw-q4vr
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
Last Updated

How to Fix CVE-2026-41149

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-2026-41149, 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 Under the default configuration, Mermaid state diagram's `classDef` allow DOM injection that escapes the SVG, although `<script>` tags are removed, preventing XSS. #### Proof-of-concept ``` stateDiagram-v2 classDef xss fill:red</style></svg><style>*{x:x;y:y;overflow:visible!important;contain:none!important;transform:none!important;filter:none!important;clip-path:none!important}</style><div style="x:x;y:y;color:red;font:5em/1 monospace;display:grid;place-items:center;z-index:2147483647;width:100vw;height:100vh;position:fixed;top:0;left:0;background:black">HACKED</div><svg><style>a:b [*] --> A:::xss ``` ### Patches - [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [37ff937f1da2e19f882fd1db01235db4d01f4056](https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056)) - [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3](https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3)) ### Workarounds If you can not update to a patched version, setting [`"securityLevel": "sandbox"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel) will prevent this, by rendering the mermaid diagram in a sandboxed `<iframe>`. ### Credits Thanks to @zsxsoft from @KeenSecurityLab for reporting this vulnerability.

CVE-2026-41149 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-ghcm-xqfw-q4vr
NVD — CVE-2026-41149 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-41149
Security Fix Commit FIX COMMIT
https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056
Security Fix Commit FIX COMMIT
https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3
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/v10.9.6
Mermaid Security Information SECURITY
https://mermaid.js.org/config/schema-docs/config.html#securitylevel

Frequently Asked Questions

What is CVE-2026-41149?
CVE-2026-41149 is a security vulnerability in Mermaid involving Improper sanitization of `classDef` in state diagrams leads to HTML 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-2026-41149?
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-2026-41149?
CVE-2026-41149 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-2026-41149?
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-ghcm-xqfw-q4vr",
  "modified" : "2026-06-08T23:21:04Z",
  "published" : "2026-05-11T19:36:46Z",
  "aliases" : [ "CVE-2026-41149" ],
  "summary" : "Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection",
  "details" : "### Impact\n\nUnder the default configuration, Mermaid state diagram's `classDef` allow DOM injection that escapes the SVG, although `<script>` tags are removed, preventing XSS.\n\n#### Proof-of-concept\n\n```\nstateDiagram-v2\n  classDef xss fill:red</style></svg><style>*{x:x;y:y;overflow:visible!important;contain:none!important;transform:none!important;filter:none!important;clip-path:none!important}</style><div style=\"x:x;y:y;color:red;font:5em/1 monospace;display:grid;place-items:center;z-index:2147483647;width:100vw;height:100vh;position:fixed;top:0;left:0;background:black\">HACKED</div><svg><style>a:b\n  [*] --> A:::xss\n```\n\n### Patches\n\n- [v11.15.0](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.15.0) (see [37ff937f1da2e19f882fd1db01235db4d01f4056](https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056))\n- [v10.9.6](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.6) (see [4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3](https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3))\n\n### Workarounds\n\nIf you can not update to a patched version, setting [`\"securityLevel\": \"sandbox\"`](https://mermaid.js.org/config/schema-docs/config.html#securitylevel)  will prevent this, by rendering the mermaid diagram in a sandboxed `<iframe>`.\n\n### Credits\n\nThanks to @zsxsoft from @KeenSecurityLab for reporting this vulnerability.",
  "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-ghcm-xqfw-q4vr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41149"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3"
  }, {
    "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/v10.9.6"
  }, {
    "type" : "WEB",
    "url" : "https://mermaid.js.org/config/schema-docs/config.html#securitylevel"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-94" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T19:36:46Z",
    "nvd_published_at" : "2026-05-22T23:16:53Z"
  }
}