How severe is CVE-2026-71437?

No CVSS score has been assigned to CVE-2026-71437 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-71437?

CVE-2026-71437 affects the following packages: mermaid (npm). Ecosystems affected: npm.

How do I fix CVE-2026-71437?

Update mermaid to 11.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-71437 is resolved across your whole dependency graph.

How do I detect CVE-2026-71437 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mermaid, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-71437 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-71437 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-71437 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-71437?

CVE-2026-71437 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 41th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-71437?

CVE-2026-71437 is classified as CWE-1321 (CWE-1321). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-71437 published, and has it been updated?

CVE-2026-71437 was published on August 6, 2026 and was last updated on September 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-71437 — mermaid

Fix: mermaid-js/mermaid@99af3fc

CVE-2026-71437 is a CWE-1321 vulnerability in mermaid. A fix is available for mermaid — see the affected versions and patch details below.

Mermaid Architecture diagrams are vulnerable to prototype pollution

Also known asGHSA-3rrr-jr9j-h3q3

Published

Aug 6, 2026

Updated

Sep 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-71437.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.14%

Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

2Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

mermaidnpm

20.3Mdownloads / week

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 [email protected]. 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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`mermaid`	≥ 11.5.0&&< 11.16.1	11.16.1`npm install mermaid@11.16.1`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mermaid, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mermaid to 11.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-71437 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This Moderate severity flaw in Mermaid Architecture Diagrams allows prototype pollution when processing specially crafted diagram text. An attacker could exploit this to corrupt application configuration, bypass security checks, or cause denial of service in Red Hat products that embed Mermaid, such as Red Hat…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-71437 (CC BY 4.0)

Frequently Asked Questions

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

O3 Security · Impact-Aware SCA

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