CVE-2025-54880 is a medium severity cross-site scripting (XSS) vulnerability affecting the mermaid-js mermaid library, specifically versions from 11.1.0 up to but not including 11.10.0. Mermaid is a JavaScript-based diagramming and charting tool that enables users to create complex diagrams using Markdown-inspired text definitions. The vulnerability arises because user-supplied input for architecture diagram icons is passed directly to the d3.js html() method without proper sanitization or neutralization. This creates a sink for reflected or stored XSS attacks, where malicious scripts can be injected and executed in the context of the user's browser. The vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. Exploitation requires no authentication but does require some user interaction (e.g., viewing a crafted diagram). The CVSS 4.0 base score is 5.1, reflecting a medium severity level due to network attack vector, low complexity, no privileges required, but user interaction needed and limited scope impact. No known exploits are currently reported in the wild. The issue was resolved in mermaid version 11.10.0 by properly sanitizing or escaping user inputs before passing them to the d3 html() method, preventing script injection. This vulnerability primarily affects web applications and services that embed or allow user-generated Mermaid diagrams with architecture icons, especially those that do not sanitize or validate input before rendering. Attackers could leverage this vulnerability to execute arbitrary JavaScript in the victim's browser, potentially leading to session hijacking, credential theft, or other client-side attacks.

For European organizations, the impact of CVE-2025-54880 depends on the extent to which they use the mermaid-js library in their web applications, documentation portals, or internal tools that allow user-generated content. Organizations in sectors with heavy reliance on technical documentation, software development, or collaborative diagramming (e.g., technology companies, engineering firms, and educational institutions) may be more exposed. Successful exploitation could lead to compromise of user sessions, theft of sensitive information, or unauthorized actions performed on behalf of users. This could result in reputational damage, regulatory non-compliance (especially under GDPR if personal data is exposed), and potential financial losses. Since the vulnerability requires user interaction, phishing or social engineering could be used to lure users into viewing malicious diagrams. The medium severity score suggests moderate risk, but the widespread adoption of Mermaid in developer tools and documentation platforms across Europe means the attack surface is non-trivial. Additionally, organizations that embed Mermaid in customer-facing portals or collaborative platforms should be particularly vigilant, as attackers could target external users to gain a foothold or escalate attacks.

1. Upgrade all instances of the mermaid-js library to version 11.10.0 or later, where the vulnerability is patched. 2. Implement strict input validation and sanitization on any user-supplied content used to generate Mermaid diagrams, especially for architecture diagram icons. Use allowlists for acceptable icon names or restrict input formats. 3. Employ Content Security Policy (CSP) headers to restrict the execution of inline scripts and reduce the impact of potential XSS exploits. 4. Monitor and audit web application logs for unusual activity or injection attempts related to Mermaid diagram rendering. 5. Educate developers and content creators about the risks of embedding user-generated content without proper sanitization. 6. If upgrading immediately is not feasible, consider disabling or restricting features that allow user input for architecture icons or rendering Mermaid diagrams until patched. 7. Conduct regular security testing, including automated scanning and manual code reviews, focusing on client-side rendering components that use Mermaid. 8. For web applications, implement robust authentication and session management to limit the damage if an XSS attack occurs.