Happy DOM is a JavaScript implementation of a web browser environment without a graphical interface, commonly used in Node.js applications for DOM manipulation and testing. Versions prior to 20.0.0 contain a critical security vulnerability (CVE-2025-61927) classified as CWE-94 (Improper Control of Generation of Code). The root cause is that the Node.js VM Context, which Happy DOM uses to execute JavaScript, is not a fully isolated sandbox. This allows malicious JavaScript code executed inside the VM Context to escape the sandbox restrictions and gain access to the underlying Node.js process environment. Specifically, in CommonJS module systems, attackers can access the require() function, enabling them to load arbitrary modules and execute arbitrary code on the host system, resulting in remote code execution (RCE). The vulnerability is worsened by the fact that JavaScript evaluation is enabled by default in Happy DOM, which may not be obvious to developers using the library. This default setting increases the risk that untrusted or malicious scripts could be executed inadvertently. The patch in Happy DOM version 20.0.0 addresses the issue by disabling JavaScript evaluation by default, thereby reducing the attack surface. The CVSS 4.0 score of 7.2 reflects a high severity, considering the network attack vector, low attack complexity, and the requirement for privileges and user interaction. Although no known exploits have been reported in the wild, the potential for exploitation exists, especially in environments where untrusted JavaScript code is processed. The vulnerability impacts confidentiality, integrity, and availability due to the possibility of arbitrary code execution on the host system. Organizations using Happy DOM in their Node.js environments should prioritize upgrading to the patched version and review their usage of JavaScript evaluation within VM contexts to prevent exploitation.

For European organizations, this vulnerability poses a significant risk, particularly for those leveraging Happy DOM in development, testing, or server-side rendering environments where untrusted JavaScript code might be executed. Successful exploitation could lead to remote code execution, allowing attackers to compromise sensitive data, manipulate application logic, or disrupt services. This could affect confidentiality by exposing sensitive information, integrity by allowing unauthorized code execution or data tampering, and availability by enabling denial-of-service attacks through system compromise. Industries with high reliance on Node.js applications, such as financial services, e-commerce, and technology sectors, are especially vulnerable. Additionally, organizations involved in software development or continuous integration pipelines using Happy DOM may inadvertently expose their infrastructure. The risk is amplified if attackers gain initial access through phishing or insider threats, as some privileges and user interaction are required. The lack of known exploits currently provides a window for proactive mitigation, but the widespread use of Node.js and JavaScript-based tools in Europe means the potential impact is broad and critical if exploited.

1. Upgrade all instances of Happy DOM to version 20.0.0 or later, where JavaScript evaluation is disabled by default, effectively mitigating the vulnerability. 2. Audit all Node.js applications and development pipelines to identify where Happy DOM is used, especially in contexts that execute untrusted or external JavaScript code. 3. Implement strict code review and validation processes to prevent untrusted code execution within Happy DOM VM contexts. 4. Where possible, isolate execution environments further by using containerization or sandboxing technologies that provide stronger isolation than Node.js VM Contexts. 5. Disable or restrict the use of CommonJS modules in environments where untrusted code execution is necessary, or switch to ESM modules with careful evaluation of their security implications. 6. Monitor application logs and system behavior for unusual activity indicative of code injection or sandbox escape attempts. 7. Educate developers and DevOps teams about the risks of enabling JavaScript evaluation by default and the importance of secure configuration. 8. Apply principle of least privilege to Node.js processes running Happy DOM to limit the potential damage from exploitation. 9. Stay informed about updates or patches from the Happy DOM project and related Node.js security advisories.