🛡️ CVE-2026-71437 — mermaid

⚪ Unknown ✅ No Known Exploit CWE-1321 NVD
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Mermaid Architecture diagrams are vulnerable to prototype pollution

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 [email protected]. 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

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity none, availability low.

Weakness class

CVE-2026-71437 is classified as CWE-1321: Prototype Pollution. Attacker input can modify an object prototype, changing behaviour for objects across the application.

Affected software

CVE-2026-71437 is recorded against 2 packages.

  • mermaid
  • unknown

Timeline and source

Published on 6 August 2026 and last revised on 7 August 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
github.com (Web)
github.com (Web)
github.com (Package)
github.com (Web)

Details

Severity Unknown
CVSS Score N/A
CVSS Vector 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
CWE CWE-1321
Public Exploit ✅ No
Source NVD
Published 2026-08-06
Updated 2026-08-12
Modified 2026-08-07
Fix URL N/A

Affected Packages

Software From version Fixed in
mermaid — —
unknown — —

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