CVE-2026-71437 Mermaid Architecture diagrams are vulnerable to prototype pollution
Attackers can pollute Object.prototype via malicious diagram text, potentially compromising the embedding application's behavior.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-71437?
CVE-2026-71437 is a medium-severity vulnerability in mermaid-js mermaid, published on 6 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. From version 11.5.0 until 11.16.1, Mermaid Architecture Diagrams are vulnerable to prototype pollution when a diagram defines a group with an id of __proto__. Because the group id is used directly as an object property key without validation, an attacker who can supply diagram text can pollute Object.prototype, potentially affecting the behavior of the embedding application. This issue is fixed in version 11.16.1.
Weakness: CWE-1321
Which versions are affected by CVE-2026-71437?
2 open source packages ship an affected version, including mermaid.
| Package | Affected | Fixed in |
|---|---|---|
mermaid npm | From 11.5.0 | 11.16.1 |
mermaid npm | From 11.5.0 | 11.16.1 |
How do I fix CVE-2026-71437?
Upgrade mermaid to 11.16.1 or later.
Is CVE-2026-71437 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-71437 exists.
Sources
Also known as CLEANSTART-2026-VN44005, DEBIAN-CVE-2026-71437, GHSA-3rrr-jr9j-h3q3, MINI-2jvp-98h4-crph, MINI-q5x3-44hg-hpmf, UBUNTU-CVE-2026-71437.