Is there a patch available for EUVD-2026-54242?

Yes, a patch is available for EUVD-2026-54242. Update the affected software to the latest version immediately.

Mermaid EUVD-2026-54242

Q: What is the CVSS score of EUVD-2026-54242?

EUVD-2026-54242 has a CVSS 4.0 base score of 6.5 (Medium). 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.3%.

| CVE-2026-71437 MEDIUM

Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution) (CWE-1321)

2026-08-06 https://github.com/mermaid-js/mermaid

GHSA-3rrr-jr9j-h3q3

RCE Denial Of Service Red Hat Prototype Pollution Suse

6.5

CVSS 4.0 · Vendor: https://github.com/mermaid-js/mermaid

Severity by source

Vendor (https://github.com/mermaid-js/mermaid) PRIMARY

6.5 MEDIUM

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

vuln.today AI

7.2 HIGH

Network-reachable via untrusted diagram input, no auth or interaction needed for automated rendering, scope changed because pollution crosses into the embedding application's realm.

3.1 AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:L

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:L

SUSE

4.3 MEDIUM

AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Red Hat

5.4 MEDIUM

qualitative

Primary rating from Vendor (https://github.com/mermaid-js/mermaid).

CVSS VectorVendor: https://github.com/mermaid-js/mermaid

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Lifecycle Timeline

CVSS changed

Aug 06, 2026 - 22:22 NVD

6.5 (MEDIUM)

Source Code Evidence Fetched

Aug 06, 2026 - 20:36 vuln.today

Analysis Generated

Aug 06, 2026 - 20:36 vuln.today

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

1 npm packages depend on mermaid (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 11.5.0.

DescriptionCVE.org

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 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

AnalysisAI

Prototype pollution in Mermaid's architecture-beta diagram renderer (mermaid@11.5.0 through 11.16.0) allows an untrusted diagram author to write the string 'horizontal' or 'vertical' directly onto Object.prototype by supplying '__proto__' as a valid group parent identifier. All JavaScript code sharing the same runtime realm that reads or enumerates the injected property name may observe corrupted option defaults, bypassed truthiness checks, or denial-of-service conditions in the embedding application. A public proof-of-concept is included in the advisory; direct remote code execution is not achievable because the injectable value is constrained to those two strings, ruling out function or object injection.

Technical ContextAI

CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes - Prototype Pollution) describes the root cause precisely: the architecture-beta diagram parser stores group parent relationships in a plain JavaScript object without sanitizing reserved keys. When a service declares 'in __proto__', the parser traverses the prototype chain and writes the layout direction property ('horizontal' or 'vertical') onto Object.prototype itself rather than a diagram-owned object. Because JavaScript's prototype chain is shared across all objects in a realm, every subsequent property lookup on an arbitrary object in the same realm may observe the injected value. The affected npm package is pkg:npm/mermaid versions >= 11.5.0 (introduced in commit cb0a4703bdf01d47508bde1c08aa9a980d70bc20) through < 11.16.1. The fix (commit 99af3fc35ef0a9a9c8c6314521344d67523ddccf, PR #8022) migrates group and service storage from plain objects to ES6 Map and Set structures, which are immune to __proto__ prototype traversal.

RemediationAI

Upgrade to mermaid@11.16.1 or later, which resolves this issue by replacing prototype-vulnerable plain-object group storage with ES6 Map and Set structures (commit 99af3fc35ef0a9a9c8c6314521344d67523ddcommit, PR https://github.com/mermaid-js/mermaid/pull/8022; release notes at https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1). The upstream advisory explicitly states there are no known workarounds short of patching. If an immediate upgrade is not possible, a compensating control is to disable or block rendering of architecture-beta diagram type at the application layer - reject or strip diagram content that begins with the 'architecture-beta' keyword before it reaches the Mermaid renderer. This eliminates exposure to this specific vector but may break legitimate architecture diagram functionality. Blanket disabling of user-submitted diagram rendering is an alternative with a higher operational cost.