GHSA-3RRR-JR9J-H3Q3
Vulnerability from github – Published: 2026-08-06 19:51 – Updated: 2026-08-06 19:51Rendering 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 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
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
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "mermaid"
},
"ranges": [
{
"events": [
{
"introduced": "11.5.0"
},
{
"fixed": "11.16.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-71437"
],
"database_specific": {
"cwe_ids": [
"CWE-1321"
],
"github_reviewed": true,
"github_reviewed_at": "2026-08-06T19:51:59Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"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",
"id": "GHSA-3rrr-jr9j-h3q3",
"modified": "2026-08-06T19:51:59Z",
"published": "2026-08-06T19:51:59Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"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",
"type": "CVSS_V4"
}
],
"summary": "Mermaid Architecture diagrams are vulnerable to prototype pollution"
}
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Nomenclature
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Vulnerability timeline
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