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.
A backport has been made for the v10 branch in c34b07a0815842327e70794d69b0c8c5a1e2a956 and was released in Mermaid 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
- liyi.zhou@sydney.edu.au (Liyi), https://lzhou1110.github.io/
- ziyue0530@gmail.com (Ziyue), https://zyy0530.github.io/
- cshe0476@uni.sydney.edu.au (Strick), https://str1ckl4nd.github.io/
- chng0012@uni.sydney.edu.au (Maurice), http://maurice.busystar.org/
- cyu210608@gmail.com (Chenchen), https://7thparkk.github.io/
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | mermaid | >= 11.0.0-alpha.1, < 11.16.1, < 10.9.8 | 11.16.1, 10.9.8 |
References
- https://github.com/mermaid-js/mermaid/security/advisories/GHSA-c4c3-pg64-4m4v
- https://github.com/mermaid-js/mermaid/pull/8022
- https://github.com/mermaid-js/mermaid/commit/2cd6dcf735533b323507e3e889ffdea870540b43
- https://github.com/mermaid-js/mermaid/commit/c34b07a0815842327e70794d69b0c8c5a1e2a956
- https://github.com/mermaid-js/mermaid
- https://github.com/mermaid-js/mermaid/releases/tag/mermaid%4011.16.1
- https://github.com/mermaid-js/mermaid/releases/tag/v10.9.8
- 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- Weakness (CWE)
CWE-1321- Platform
- npm
- Package
mermaid- Disclosed
- 06.08.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-c4c3-pg64-4m4v - CC BY 4.0
Vulnerability history: mermaid
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 16
- First → latest
- 09.2020 08.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 3
- Medium 12
- Low 1
Disclosures per year
- 2020: 1
- 2021: 1
- 2022: 2
- 2023: 0
- 2024: 1
- 2025: 2
- 2026: 9
-
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