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🛡️ CVE-2026-71438 — mermaid

🟢 CVSS 2.0 — Low ✅ No Known Exploit CWE-1321 NVD
2.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Mermaid configuration APIs allow prototype pollution

Summary

Mermaid's configuration setters (mermaid.initialize, mermaidAPI.setConfig, and mermaidAPI.updateSiteConfig) merge the caller-supplied configuration object into Mermaid's internal config using the assignWithDepth deep-merge helper that is vulnerable to prototype pollution.

Because these APIs are intended to receive trusted configuration supplied by the application integrating Mermaid, Mermaid assesses the practical risk as low. The vulnerability is only reachable if an application forwards attacker-controlled data directly into one of these configuration entry points, which is outside their documented usage.

User-controlled configuration (e.g. configuration in diagram code using %%{init: {}}%% or YAML frontmatter) are already protected from prototype pollution.

Patches

This has been patched in https://github.com/mermaid-js/mermaid/commit/2cd6dcf735533b323507e3e889ffdea870540b43 and released in [Mermaid v11.16.1](https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1).

A backport has been made for the v10 branch in c34b07a0815842327e70794d69b0c8c5a1e2a956 and was released in [Mermaid v10.9.8](https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8)

Impact

Mermaid believes it's unlikely that anybody is impacted, as these functions are configuration entry points expected to receive trusted, developer-controlled values as they can modify other security-relevant configuration.

Workarounds

Don't pass user-controlled data to the mermaid.initialize, mermaidAPI.setConfig, and mermaidAPI.updateSiteConfig functions. Instead, users can use %%{init: {}}%% or YAML frontmatter in diagrams.

Reporters

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs administrative privileges on the target. A user must actively cooperate. Rated impact: confidentiality none, integrity low, availability low.

CVSS metrics in full

The score comes from this vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:A/VC:N/VI:L/VA:L/SC:H/SI:H/SA:H

  • Attack vector: Local — a local account, shell or session on the host is needed.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: Present — the target has to be in a particular state for the attack to work.
  • Privileges required: High — administrative rights are needed first.
  • User interaction: Active — the victim has to cooperate with the attack.
  • Confidentiality impact: None.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: Low — limited, and the attacker does not choose what is affected.

Weakness class

CVE-2026-71438 is classified as CWE-1321: Prototype Pollution. Attacker input can modify an object prototype, changing behaviour for objects across the application.

Affected software

CVE-2026-71438 is recorded against 2 packages.

  • mermaid
  • unknown

Timeline and source

Published on 6 August 2026 and last revised on 7 August 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
github.com (Web)
github.com (Web)
github.com (Web)
github.com (Package)
github.com (Web)
github.com (Web)

Other advisories for this package

mermaid has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-1321: Prototype Pollution) in other software:

Details

Severity LOW
CVSS Score 2.0
CVSS Vector CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:A/VC:N/VI:L/VA:L/SC:H/SI:H/SA:H
CWE CWE-1321
Public Exploit ✅ No
Source NVD
Published 2026-08-06
Updated 2026-08-20
Modified 2026-08-07
Fix URL N/A

Affected Packages

Software From version Fixed in
mermaid — —
unknown — —

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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