CVE-2021-43861 Incorrect sanitisation function leads to `XSS`

What is CVE-2021-43861?

CVE-2021-43861 is a high-severity cross-site scripting vulnerability in mermaid-js mermaid, published on 30 Dec 2021. An attacker needs administrator access to exploit it, with no action from the victim.

Official description

Mermaid is a Javascript based diagramming and charting tool that uses Markdown-inspired text definitions and a renderer to create and modify complex diagrams. Prior to version 8.13.8, malicious diagrams can run javascript code at diagram readers' machines. Users should upgrade to version 8.13.8 to receive a patch. There are no known workarounds aside from upgrading.

Weakness: CWE-79, CWE-20

Which versions are affected by CVE-2021-43861?

2 open source packages ship an affected version, including mermaid. It affects 1 product.

Products include Mermaid Project Mermaid.

How do I fix CVE-2021-43861?

Upgrade mermaid to 8.13.8 or later.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2021-43861 being exploited?

There is no known exploitation of CVE-2021-43861 in the wild and no public exploit code.

Other vulnerabilities in mermaid-js mermaid

• CVE-2021-35513 Cross-site Scripting in Mermaid Medium 6.1
• CVE-2026-41150 Mermaid Gantt Charts are vulnerable to an Infinite Loop DoS Medium 5.3
• CVE-2026-41159 Mermaid: Improper sanitization of configuration leads to CSS injection Medium 5.3
• CVE-2025-54880 Mermaid does not properly sanitize architecture diagram iconText leading to XSS Medium 5.1
• CVE-2022-31108 Arbitrary `CSS` injection into the generated graph affecting the container HTML in mermaid.js Medium 4.1

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-43861, GHSA-p3rp-vmj9-gv6v, UBUNTU-CVE-2021-43861.