Vulnerability · Published May 22, 2026 · Assigned by GitHub_M

CVE-2026-41149Mermaid: Improper sanitization of `classDef` in state diagrams leads to HTML injection

Medium 5.3

In plain English

A medium-severity code injection in mermaid from mermaid-js. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.3Medium

Exploit odds (30 days)0.4%top 65.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Versions 10.9.5 and earlier, as well as 11.0.0-alpha.1 through 11.14.0, are vulnerable to HTML injection under the default configuration. Specifically, the classDef directive in Mermaid state diagrams permits DOM injection that escapes the SVG context. However, <script> tags are stripped, which prevents cross-site scripting (XSS). This issue has been fixed in versions 10.9.6 and 11.15.0. If developers are unable to immediately upgrade, they can work around this issue by setting "securityLevel": "sandbox", which prevents the issue by rendering the mermaid diagram in a sandboxed <iframe>.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	node-mermaid	no fix listed	DEBIAN-CVE-2026-41149
Ubuntu:22.04:LTS	node-mermaid	no fix listed	UBUNTU-CVE-2026-41149
Ubuntu:26.10	node-mermaid	no fix listed	UBUNTU-CVE-2026-41149
npm	mermaid	11.15.0	GHSA-ghcm-xqfw-q4vr
npm	mermaid	10.9.6	GHSA-ghcm-xqfw-q4vr

Affected products (as reported)

Vendor	Product	Versions
mermaid-js	mermaid	>= 11.0.0-alpha.1, < 11.15.0< 10.9.6

Weakness: CWE-94 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:L

References

https://github.com/mermaid-js/mermaid/security/advisories/GHSA-ghcm-xqfw-q4vr x_refsource_CONFIRM
https://github.com/mermaid-js/mermaid/commit/37ff937f1da2e19f882fd1db01235db4d01f4056 x_refsource_MISC
https://github.com/mermaid-js/mermaid/commit/4e2d512bf5bf6f9de1a8f0a48da78dc4d09ac4f3 x_refsource_MISC