mermaid-js mermaid up to 10.9.5/11.14.x createCssStyles Parser addStyleClass code injection

Summaryinfo

A vulnerability categorized as critical has been discovered in mermaid-js mermaid up to 10.9.5/11.14.x. Impacted is the function addStyleClass of the component createCssStyles Parser. Such manipulation leads to code injection. This vulnerability is uniquely identified as CVE-2026-41148. The attack can be launched remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in mermaid-js mermaid up to 10.9.5/11.14.x. It has been rated as critical. Affected by this issue is the function addStyleClass of the component createCssStyles Parser. The manipulation with an unknown input leads to a code injection vulnerability. Using CWE to declare the problem leads to 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. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Versions 10.9.5 and prior, in addition to 11.0.0-alpha.1 through 11.12.0 are vulnerable to CSS injection through improper sanitization. The state diagram (and any other diagram type that routes user-controlled style strings through the createCssStyles parser) captures classDef values using an unrestricted regex that matches everything up to a newline. That value then flows unsanitized through addStyleClass() into createCssStyles() and is assigned to style.innerHTML, so a closing brace (}) in the value terminates the generated CSS selector and turns everything after it into a new CSS rule on the page. This enables page defacement, user tracking via url() callbacks, and DOM attribute exfiltration. 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 .

The advisory is available at github.com. This vulnerability is handled as CVE-2026-41148 since 04/17/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Successful exploitation requires user interaction by the victim. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1059 by the MITRE ATT&CK project.

The vulnerability scanner Nessus provides a plugin with the ID 316560 (Linux Distros Unpatched Vulnerability : CVE-2026-41148), 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 upgrade is hosted for download at github.com. Applying the patch 8fead23c59166b7bab6a39eac81acebee2859102 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (316560). If you want to get best quality of vulnerability data, you may have to visit VulDB.

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

License

• open-source

Website

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

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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