CVE-2025-34146 is a prototype pollution vulnerability identified in the @nyariv/sandboxjs JavaScript sandboxing library, affecting all versions up to and including 0.8.23. Prototype pollution occurs when an attacker is able to inject or modify properties on JavaScript's Object.prototype, which is the base object from which most objects inherit. In this case, the vulnerability arises due to insufficient checks on prototype access within the sandbox's executor logic, particularly when handling JavaScript function objects returned by the sandboxed code. This flaw allows an attacker to craft malicious JavaScript code that can inject arbitrary properties into Object.prototype, thereby altering the behavior of all objects in the runtime environment. The consequences of this vulnerability include the potential for denial-of-service (DoS) conditions, where the application or service crashes or becomes unresponsive due to corrupted object states. More critically, under certain conditions, the attacker may be able to escape the sandbox environment, which is designed to restrict and isolate code execution. Escaping the sandbox could allow execution of arbitrary code outside the intended constraints, leading to further compromise of the host system or application. The vulnerability has been assigned a CVSS 4.0 base score of 7.0 (high severity), reflecting its significant impact on confidentiality and integrity, with no required privileges or user interaction for exploitation. No known exploits are currently reported in the wild, and no patches have been published at the time of disclosure. The root cause is the improper control of modification of object prototype attributes (CWE-1321), a common issue in JavaScript environments that do not adequately validate or sanitize prototype manipulations. Given the widespread use of JavaScript sandboxes in web applications, server-side environments, and development tools, this vulnerability poses a substantial risk to applications relying on @nyariv/sandboxjs for secure code execution isolation.

For European organizations, the impact of CVE-2025-34146 can be significant, especially those utilizing @nyariv/sandboxjs in their web applications, cloud services, or internal development tools. Exploitation could lead to denial-of-service conditions, disrupting business operations and causing service outages. More severe is the potential sandbox escape, which could allow attackers to execute arbitrary code on the host system, leading to data breaches, unauthorized access to sensitive information, and potential lateral movement within corporate networks. This risk is heightened in sectors with stringent data protection requirements such as finance, healthcare, and critical infrastructure, where confidentiality and integrity are paramount. Additionally, the vulnerability could be leveraged to bypass security controls that rely on sandboxing for code isolation, undermining trust in application security measures. The lack of required privileges or user interaction means that attackers could exploit this vulnerability remotely and autonomously, increasing the threat level. European organizations operating in cloud environments or offering SaaS solutions that embed this library are particularly vulnerable, as a successful attack could compromise multiple tenants or customers. Furthermore, regulatory frameworks like GDPR impose strict obligations on data protection and breach notification, so exploitation could result in legal and financial repercussions.

To mitigate CVE-2025-34146, European organizations should first identify all instances where @nyariv/sandboxjs is used within their software stack. Immediate steps include: 1) Applying any available patches or updates from the vendor once released. Since no patches are currently available, organizations should monitor vendor channels closely. 2) Implement strict input validation and sanitization on any user-supplied code or data executed within the sandbox to reduce the risk of malicious prototype pollution payloads. 3) Employ runtime monitoring and anomaly detection to identify unusual prototype modifications or sandbox escape attempts. 4) Consider isolating sandbox execution environments further using containerization or virtual machines to limit the blast radius if an escape occurs. 5) Review and harden the security posture of applications relying on sandboxjs by minimizing privileges and access rights of the sandboxed environment. 6) If feasible, temporarily replace or avoid using @nyariv/sandboxjs until a secure version is available, or evaluate alternative sandboxing solutions with robust prototype pollution protections. 7) Conduct thorough security testing including fuzzing and code review focused on prototype pollution vectors. 8) Educate developers about the risks of prototype pollution and secure coding practices related to JavaScript object manipulation. These measures, combined, will reduce the likelihood and impact of exploitation.