CVE-2026-71437: CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in mermaid-js mermaid
Mermaid versions from 11.5.0 up to but not including 11.16.1 are vulnerable to prototype pollution via the Architecture Diagrams feature. This occurs when a diagram defines a group with an id of __proto__, which is used directly as an object property key without validation. An attacker able to supply diagram text can exploit this to modify Object.prototype, potentially altering the behavior of the embedding application. The vulnerability is fixed in version 11.16.1.
AI Analysis
Technical Summary
Mermaid-js's mermaid tool versions >=11.5.0 and <11.16.1 contain a prototype pollution vulnerability (CWE-1321) in the Architecture Diagrams feature. Specifically, when a group is defined with an id of __proto__, this id is used as an object property key without validation, allowing an attacker who can control diagram text input to pollute Object.prototype. This can affect the embedding application's behavior. The issue is resolved in version 11.16.1.
Potential Impact
An attacker who can supply malicious diagram text can exploit this vulnerability to modify Object.prototype, which may lead to unexpected behavior or security issues in the embedding application. The CVSS 4.0 score is 6.5 (medium severity), indicating a moderate impact with network attack vector, low privileges required, no user interaction, and limited impact on confidentiality, integrity, and availability.
Mitigation Recommendations
Upgrade Mermaid to version 11.16.1 or later, where this prototype pollution vulnerability is fixed. No other official remediation or temporary fixes are indicated. Patch status is confirmed by the version range and fix version stated.
CVE-2026-71437: CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in mermaid-js mermaid
Description
Mermaid versions from 11.5.0 up to but not including 11.16.1 are vulnerable to prototype pollution via the Architecture Diagrams feature. This occurs when a diagram defines a group with an id of __proto__, which is used directly as an object property key without validation. An attacker able to supply diagram text can exploit this to modify Object.prototype, potentially altering the behavior of the embedding application. The vulnerability is fixed in version 11.16.1.
CVSS v4.0
Score 6.5medium
Affected software
mermaid-js
mermaid
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Mermaid-js's mermaid tool versions >=11.5.0 and <11.16.1 contain a prototype pollution vulnerability (CWE-1321) in the Architecture Diagrams feature. Specifically, when a group is defined with an id of __proto__, this id is used as an object property key without validation, allowing an attacker who can control diagram text input to pollute Object.prototype. This can affect the embedding application's behavior. The issue is resolved in version 11.16.1.
Potential Impact
An attacker who can supply malicious diagram text can exploit this vulnerability to modify Object.prototype, which may lead to unexpected behavior or security issues in the embedding application. The CVSS 4.0 score is 6.5 (medium severity), indicating a moderate impact with network attack vector, low privileges required, no user interaction, and limited impact on confidentiality, integrity, and availability.
Mitigation Recommendations
Upgrade Mermaid to version 11.16.1 or later, where this prototype pollution vulnerability is fixed. No other official remediation or temporary fixes are indicated. Patch status is confirmed by the version range and fix version stated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-06T16:28:51.183Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a75070fbf8831d5395f5dd5
Added to database: 08/06/2026, 22:13:35 UTC
Last enriched: 08/14/2026, 16:03:10 UTC
Last updated: 09/21/2026, 22:01:37 UTC
Views: 51
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