mermaid-js mermaid up to 10.9.5/11.14.x Diagram has code injection

Summaryinfo

A vulnerability was found in mermaid-js mermaid up to 10.9.5/11.14.x. It has been declared as critical. Impacted is the function has of the component Diagram Handler. Executing a manipulation can lead to code injection. This vulnerability is registered as CVE-2026-41159. It is possible to launch the attack remotely. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in mermaid-js mermaid up to 10.9.5/11.14.x and classified as critical. This vulnerability affects the function has of the component Diagram Handler. The manipulation with an unknown input leads to a code injection vulnerability. The CWE definition for the vulnerability is CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.6 and 11.15.0, Mermaid's default configuration allows injecting CSS that applies outside of the Mermaid diagram via the fontFamily, themeCSS, and altFontFamily configuration options. The injected CSS exploits stylis's & (scope reference) handling. :not(&) escapes the #mermaid-xxx automatic scoping, applying styles to all page elements. Global at-rules (@font-face, @keyframes, @counter-style) are also injectable as stylis hoists them to top level. This allows page defacement and DOM attribute exfiltration via CSS :has() selectors. This vulnerability is fixed in 10.9.6 and 11.15.0.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-41159 since 04/17/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1059.

The vulnerability scanner Nessus provides a plugin with the ID 318018 (Linux Distros Unpatched Vulnerability : CVE-2026-41159), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 10.9.6 or 11.15.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (318018). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

• mermaid-js

Name

• mermaid

Version

• 10.9.0
• 10.9.1
• 10.9.2
• 10.9.3
• 10.9.4
• 10.9.5
• 11.0
• 11.1
• 11.2
• 11.3
• 11.4
• 11.5
• 11.6
• 11.7
• 11.8
• 11.9
• 11.10
• 11.11
• 11.12
• 11.13
• 11.14

Website

• Product: https://github.com/mermaid-js/mermaid/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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