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 contain a prototype pollution vulnerability in the handling of Architecture Diagrams. Specifically, if a diagram defines a group with an id of __proto__, this id is used directly as an object property key without validation, allowing an attacker supplying diagram text to modify Object.prototype. This vulnerability is fixed in version 11.16.1.
AI Analysis
Technical Summary
The vulnerability in mermaid-js mermaid affects versions >=11.5.0 <11.16.1 and involves improper control of object prototype attributes (CWE-1321). When a diagram defines a group with an id of __proto__, this id is used as a property key on an object without validation, enabling prototype pollution. This can alter the behavior of the embedding application by modifying Object.prototype. The issue is resolved in version 11.16.1.
Potential Impact
An attacker able to supply diagram text can exploit this vulnerability to pollute Object.prototype, potentially causing unexpected behavior or security issues in the embedding application. The CVSS 4.0 score is 6.5 (medium severity), indicating a moderate risk with network attack vector, low attack complexity, no privileges or user interaction required, but limited to low impact on availability and integrity with high scope and security requirements.
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 vendor advisory stating the fix is in 11.16.1.
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 contain a prototype pollution vulnerability in the handling of Architecture Diagrams. Specifically, if a diagram defines a group with an id of __proto__, this id is used directly as an object property key without validation, allowing an attacker supplying diagram text to modify Object.prototype. This vulnerability is fixed in version 11.16.1.
CVSS v4.0
Score 6.5medium
Affected software
Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in mermaid-js mermaid affects versions >=11.5.0 <11.16.1 and involves improper control of object prototype attributes (CWE-1321). When a diagram defines a group with an id of __proto__, this id is used as a property key on an object without validation, enabling prototype pollution. This can alter the behavior of the embedding application by modifying Object.prototype. The issue is resolved in version 11.16.1.
Potential Impact
An attacker able to supply diagram text can exploit this vulnerability to pollute Object.prototype, potentially causing unexpected behavior or security issues in the embedding application. The CVSS 4.0 score is 6.5 (medium severity), indicating a moderate risk with network attack vector, low attack complexity, no privileges or user interaction required, but limited to low impact on availability and integrity with high scope and security requirements.
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 vendor advisory stating the fix is in 11.16.1.
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
- Remediation Level
- null
Threat ID: 6a75070fbf8831d5395f5dd5
Added to database: 08/06/2026, 22:13:35 UTC
Last enriched: 08/06/2026, 22:28:24 UTC
Last updated: 08/07/2026, 01:08:05 UTC
Views: 4
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.