---
id: CVE-2026-71438
title: >-
  Mermaid is a JavaScript tool that uses Markdown-inspired text to create and
  modify diagrams and charts
summary: >-
  Mermaid is a JavaScript tool that uses Markdown-inspired text to create and
  modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid's
  configuration setters (mermaid.initialize, mermaidAPI.setConfig, and
  mermaidAPI.updateSiteConf…
severity: low
cwe:
  - CWE-1321
vendor: mermaid
product: mermaid
affected:
  - 'mermaid >= 11.0.0-alpha.1, < 11.16.1'
  - mermaid < 10.9.8
patched:
  - mermaid 11.16.1
  - mermaid 10.9.8
published: '2026-08-06'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:53:06.753'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-71438'
references:
  - url: >-
      https://github.com/mermaid-js/mermaid/commit/2cd6dcf735533b323507e3e889ffdea870540b43
    label: security-advisories@github.com
  - url: >-
      https://github.com/mermaid-js/mermaid/commit/c34b07a0815842327e70794d69b0c8c5a1e2a956
    label: security-advisories@github.com
  - url: 'https://github.com/mermaid-js/mermaid/pull/8022'
    label: security-advisories@github.com
  - url: 'https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1'
    label: security-advisories@github.com
  - url: 'https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8'
    label: security-advisories@github.com
  - url: >-
      https://github.com/mermaid-js/mermaid/security/advisories/GHSA-c4c3-pg64-4m4v
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-c4c3-pg64-4m4v'
tags:
  - nvd
  - ghsa
  - npm
epss: 0.00353
epssPercentile: 0.26325
aliases:
  - GHSA-c4c3-pg64-4m4v
ecosystem: npm
ingestedAt: '2026-08-06T20:03:56.356Z'
---

## Overview

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid's configuration setters (mermaid.initialize, mermaidAPI.setConfig, and mermaidAPI.updateSiteConfig) merge caller-supplied configuration into Mermaid's internal config using the assignWithDepth deep-merge helper, which is vulnerable to prototype pollution. This is only exploitable if an application forwards untrusted data directly into one of these configuration entry points, which is outside their documented usage; diagram-supplied configuration (e.g. %%{init: {}}%% or YAML frontmatter) is not affected. This issue is fixed in versions 10.9.8 and 11.16.1.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-71438)

Affected packages:

- `mermaid >= 11.0.0-alpha.1, < 11.16.1`
- `mermaid < 10.9.8`

Patched in:

- `mermaid 11.16.1`
- `mermaid 10.9.8`

Source: https://github.com/advisories/GHSA-c4c3-pg64-4m4v