Vulnerability · Published Aug 6, 2026 · Assigned by GitHub_M
CVE-2026-71438Mermaid configuration APIs allow prototype pollution
Low 2.4
In plain English
A low-severity prototype pollution in mermaid from mermaid-js. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid's configuration setters (mermaid.initialize, mermaidAPI.setConfig, and mermaidAPI.updateSiteConfig) merge caller-supplied configuration into Mermaid's internal config using the assignWithDepth deep-merge helper, which is vulnerable to prototype pollution. This is only exploitable if an application forwards untrusted data directly into one of these configuration entry points, which is outside their documented usage; diagram-supplied configuration (e.g. %%{init: {}}%% or YAML frontmatter) is not affected. This issue is fixed in versions 10.9.8 and 11.16.1.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:14 | node-mermaid | no fix listed | DEBIAN-CVE-2026-71438 |
| Ubuntu:22.04:LTS | node-mermaid | no fix listed | UBUNTU-CVE-2026-71438 |
| Ubuntu:26.10 | node-mermaid | no fix listed | UBUNTU-CVE-2026-71438 |
| npm | mermaid | 11.16.1 | GHSA-c4c3-pg64-4m4v |
| npm | mermaid | 10.9.8 | GHSA-c4c3-pg64-4m4v |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| mermaid-js | mermaid | < 10.9.8>= 11.0.0-alpha.1, < 11.16.1 |
Weakness: CWE-1321 · 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
References
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-c4c3-pg64-4m4v x_refsource_CONFIRM
- https://github.com/mermaid-js/mermaid/pull/8022 x_refsource_MISC
- https://github.com/mermaid-js/mermaid/commit/2cd6dcf735533b323507e3e889ffdea870540b43 x_refsource_MISC
- https://github.com/mermaid-js/mermaid/commit/c34b07a0815842327e70794d69b0c8c5a1e2a956 x_refsource_MISC
- https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1 x_refsource_MISC
- https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8 x_refsource_MISC