CVE-2026-71437: Mermaid Mermaid Architecture Diagrams Are Vulnerable Vulnerability

MODERATE
Advisory Identifier: GHSA-3rrr-jr9j-h3q3
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CWE-1321
Published
Advisory Summary

CVE-2026-71437 is a MODERATE mermaid architecture diagrams are vulnerable vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting Mermaid libraries in the npm ecosystem. The issue involves mermaid architecture diagrams are vulnerable to prototype pollution. Remediation is available by upgrading affected packages to version 11.16.1.

CVE-2026-71437 at a Glance

CVE Identifier CVE-2026-71437
GHSA Identifier GHSA-3rrr-jr9j-h3q3
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product Mermaid
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-71437

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: 11.16.1 
npm install mermaid@11.16.1
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-2026-71437, 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 11.16.1), 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-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. 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

Rendering an untrusted `architecture-beta` diagram lets the diagram author write an arbitrary property with the value `horizontal` or `vertical` onto `Object.prototype`. A group id of `__proto__` is accepted as a valid parent. ### Impact Any code in the same realm that reads a property of that name from an arbitrary object, or enumerates an object with bare `for...in`, observes the injected value (which can only be the string `horizontal` or `vertical`. This may mean corrupted option/config defaults, bypassed truthiness checks, causing denial of service or logic corruption in the embedding application. Because the injected value cannot be an object or function, this is not directly exploitable for remote code execution. ### PoC ``` architecture-beta group mermaidPrototypePollutionMarker(cloud)[Marker] service a(server)[A] in __proto__ service b(server)[B] in mermaidPrototypePollutionMarker a:R -- L:b ``` The vulnerable write was introduced in commit [cb0a4703bdf01d47508bde1c08aa9a980d70bc20](https://github.com/mermaid-js/mermaid/commit/cb0a4703bdf01d47508bde1c08aa9a980d70bc20) and first shipped in `mermaid@11.5.0`. The lines are unchanged in every release since. ### Patches This has been patched by https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf, released in [Mermaid v11.16.1](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1) ### Workarounds There are no known workarounds. Please update to a patched version. ### References _Are there any links users can visit to find out more?_ - https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf - https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1

CVE-2026-71437 Affected Mermaid Versions

1 component(s)
Fixed Versions:
11.16.1
Product / Package Ecosystem Affected Versions Fixed Version
mermaid
npm/mermaid
npm
≥ 11.5.0
< 11.16.1
11.16.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/mermaid-js/mermaid/security/advisories/GHSA-3rrr-jr9j-h3q3
Mermaid Source Repository REPOSITORY
https://github.com/mermaid-js/mermaid/pull/8022
Security Fix Commit FIX COMMIT
https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf
Mermaid Source Repository REPOSITORY
https://github.com/mermaid-js/mermaid
Mermaid Release RELEASE
https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.16.1

Frequently Asked Questions

What is CVE-2026-71437?
CVE-2026-71437 is a security vulnerability in Mermaid involving Mermaid Architecture diagrams are vulnerable to prototype pollution under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which Mermaid versions are affected?
Affected versions include releases prior to 11.16.1 across affected packages: mermaid.
What version fixes CVE-2026-71437?
Upgrading to 11.16.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is mermaid affected?
Yes, mermaid is affected in releases prior to 11.16.1. Upgrade your dependency to 11.16.1 or later.
What CWE is associated with CVE-2026-71437?
CVE-2026-71437 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check npm dependencies for CVE-2026-71437?
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-3rrr-jr9j-h3q3",
  "modified" : "2026-08-06T19:51:59Z",
  "published" : "2026-08-06T19:51:59Z",
  "aliases" : [ "CVE-2026-71437" ],
  "summary" : "Mermaid Architecture diagrams are vulnerable to prototype pollution",
  "details" : "Rendering an untrusted `architecture-beta` diagram lets the diagram author write an arbitrary property with the value `horizontal` or `vertical` onto `Object.prototype`. A group id of `__proto__` is accepted as a valid parent.\n\n### Impact\n\nAny code in the same realm that reads a property of that name from an arbitrary object, or enumerates an object with bare `for...in`, observes the injected value (which can only be the string `horizontal` or `vertical`.\n\nThis may mean corrupted option/config defaults, bypassed truthiness checks, causing denial of service or logic corruption in the embedding application.\n\nBecause the injected value cannot be an object or function, this is not directly exploitable for remote code execution.\n\n### PoC\n\n```\narchitecture-beta\n      group mermaidPrototypePollutionMarker(cloud)[Marker]\n      service a(server)[A] in __proto__\n      service b(server)[B] in mermaidPrototypePollutionMarker\n      a:R -- L:b\n```\n\nThe vulnerable write was introduced in commit [cb0a4703bdf01d47508bde1c08aa9a980d70bc20](https://github.com/mermaid-js/mermaid/commit/cb0a4703bdf01d47508bde1c08aa9a980d70bc20) and first shipped in `mermaid@11.5.0`. The lines are unchanged in every release since.\n\n### Patches\n\nThis has been patched by https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf, released in [Mermaid v11.16.1](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1)\n\n### Workarounds\n\nThere are no known workarounds. Please update to a patched version.\n\n### References\n\n_Are there any links users can visit to find out more?_\n\n- https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf\n- https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:H/SI:H/SA:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "mermaid"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "11.5.0"
      }, {
        "fixed" : "11.16.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/security/advisories/GHSA-3rrr-jr9j-h3q3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/pull/8022"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mermaid-js/mermaid"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.16.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-06T19:51:59Z",
    "nvd_published_at" : null
  }
}