What’s Vulnerable › Vulnerabilities

CVE-2026-71437: Mermaid Architecture diagrams are vulnerable to prototype pollution

• Severity: medium (CVSS 6.5 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-06 · updated 2026-10-24
• Weakness: CWE-1321

Description

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. From version 11.5.0 until 11.16.1, Mermaid Architecture Diagrams are vulnerable to prototype pollution when a diagram defines a group with an id of __proto__. Because the group id is used directly as an object property key without validation, an attacker who can supply diagram text can pollute Object.prototype, potentially affecting the behavior of the embedding application. This issue is fixed in version 11.16.1.

Affected products

• mermaid-js mermaid: from 11.5.0, < 11.16.1

References

• https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccf
• https://github.com/mermaid-js/mermaid/pull/8022
• https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.16.1
• https://github.com/mermaid-js/mermaid/security/advisories/GHSA-3rrr-jr9j-h3q3
• https://github.com/mermaid-js/mermaid/security/advisories/GHSA-3rrr-jr9j-h3q3

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