CVE-2026-71437
mediumpriority · track · 0EPSS 0.005 · 43 %ileEUUSEPSS · scored 2026-10-27
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.
cvss
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · low–medium · 2.6–6.5
ssvc
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weaknesses
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affected products (2)
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advisories (1)
Vendor and ecosystem advisories describing this.
- GHSA-3rrr-jr9j-h3q3Mermaid Architecture diagrams are vulnerable to prototype pollution2026-08-06ghsa · osvUS
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
also known as (3)
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sources
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references (13)
External citations — patches, advisories, analysis.
- https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccfcnnvd
- https://github.com/mermaid-js/mermaid/pull/8022cnnvd
- https://github.com/mermaid-js/mermaid/releasesPatchcnnvd
- https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.16.1cnnvd
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-3rrr-jr9j-h3q3cnnvd
- https://github.com/mermaid-js/mermaid/commit/99af3fc35ef0a9a9c8c6314521344d67523ddccfenisa_euvd
- https://github.com/mermaid-js/mermaid/pull/8022enisa_euvd
- https://github.com/mermaid-js/mermaid/releases/tag/mermaid@11.16.1enisa_euvd
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