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GHSA-3rrr-jr9j-h3q3 CVE-2026-71437

Mermaid Architecture diagrams are vulnerable to prototype pollution

Medium npm
Severity
6.5 / 10
Medium · CVSS 4.0
Exploit chance (EPSS)
0.50%
Chance of exploitation in the next 30 days. Higher than 43.07% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-1321 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Fix
11.16.1
Upgrade mermaid to this version or later

Description

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?

Affected versions

npm

PackageVulnerableFixed in
mermaid
>= 11.5.0, < 11.16.1
11.16.1
mermaid
>= 11.5.0, < 11.16.1
11.16.1

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

mermaid npm → 11.16.1

npm
npm install mermaid@11.16.1
yarn
yarn add mermaid@11.16.1
pnpm
pnpm add mermaid@11.16.1

Severity breakdown

CVSS 4.0 6.5

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

Attack vector
Network
Attack complexity
Low
Attack requirements
None
Privileges required
Low
User interaction
None
Confidentiality (vulnerable system)
None
Integrity (vulnerable system)
None
Availability (vulnerable system)
Low
Confidentiality (subsequent systems)
High
Integrity (subsequent systems)
High
Availability (subsequent systems)
High

Weakness

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

The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.

How to prevent it
  • Implementation: By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
  • Architecture and Design: By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
  • Implementation: When handling untrusted objects, validating using a schema can be used.
  • Implementation: By using an object without prototypes (via Object.create(null) ), adding object prototype attributes by accessing the prototype via the special attributes becomes impossible, mitigating this weakness.
  • Implementation: Map can be used instead of objects in most cases. If Map methods are used instead of object attributes, it is not possible to access the object prototype or modify it.

References

Advisories

Fixes and patches

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-rhh3-jpg6-66xh
Mermaid radar diagrams are vulnerable to DoS
Medium Also affects mermaid
GHSA-c4c3-pg64-4m4v
Mermaid configuration APIs allow prototype pollution
Low Also affects mermaid
GHSA-6x64-9x62-f2gx
Mermaid allows CSS injection applying to sibling elements of the diagram
Medium Also affects mermaid
GHSA-2v8p-3f2j-5mp7
Mermaid XY Charts are vulnerable to an infinite loop DoS
Medium Also affects mermaid
GHSA-87f9-hvmw-gh4p
Mermaid: Improper sanitization of configuration leads to CSS injection
Medium Also affects mermaid
GHSA-6m6c-36f7-fhxh
Mermaid Gantt Charts are vulnerable to an Infinite Loop DoS
Medium Also affects mermaid
GHSA-ghcm-xqfw-q4vr
Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection
Medium Also affects mermaid
GHSA-xcj9-5m2h-648r
Mermaid: Improper sanitization of `classDefs` in diagrams leads to CSS injection
Medium Also affects mermaid

Credits: ThomasRinsma, aloisklink, jkim-notion

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