CVE-2026-23736 identifies a prototype pollution vulnerability in the seroval JavaScript library, specifically affecting versions 1.4.0 and earlier. Seroval is designed to facilitate JavaScript value stringification, including complex structures that exceed the capabilities of the native JSON.stringify method. The vulnerability stems from inadequate input validation during the JSON deserialization process, where maliciously crafted object keys can modify the prototype of base JavaScript objects. This improper control over prototype attributes (classified under CWE-1321) allows attackers to inject or alter properties on Object.prototype, potentially influencing all objects inheriting from it. Such prototype pollution can lead to unexpected behavior, including data corruption, bypassing security controls, or triggering denial-of-service conditions. The vulnerability is exploitable remotely over the network without requiring authentication or user interaction, increasing its risk profile. The CVSS v3.1 base score of 7.3 reflects a high severity due to its potential impact on confidentiality, integrity, and availability. The issue is confined to the JSON deserialization functionality of seroval and has been addressed in version 1.4.1. No public exploits have been reported to date, but the ease of exploitation and the widespread use of JavaScript libraries in web applications make this a significant threat vector.

For European organizations, the vulnerability poses a substantial risk, particularly for those developing or deploying web applications and backend services that utilize the seroval library for JSON processing. Prototype pollution can lead to data integrity issues, unauthorized data access, or application crashes, affecting service availability and trustworthiness. Industries such as finance, healthcare, and critical infrastructure, which rely heavily on secure data processing, could face operational disruptions or data breaches. The network-exploitable nature means attackers can target exposed services remotely, increasing the attack surface. Additionally, the widespread adoption of JavaScript and Node.js in European software ecosystems amplifies the potential impact. Organizations failing to patch may experience reputational damage, regulatory penalties under GDPR for data breaches, and increased remediation costs. The absence of known exploits currently provides a window for proactive mitigation but also underscores the need for vigilance as exploit development could emerge rapidly.

European organizations should immediately upgrade all instances of seroval to version 1.4.1 or later to remediate the vulnerability. Beyond patching, developers must audit all JSON deserialization code paths to ensure that untrusted input is never directly deserialized without strict validation or sanitization. Implementing runtime protections such as prototype pollution detection libraries or employing secure coding practices that avoid direct prototype manipulation can further reduce risk. Network-level controls, including web application firewalls (WAFs), should be configured to detect and block suspicious payloads targeting JSON deserialization endpoints. Continuous monitoring for anomalous application behavior indicative of prototype pollution exploitation is recommended. Security teams should also review dependency management processes to ensure timely updates of third-party libraries. Finally, conducting threat modeling and penetration testing focused on deserialization vulnerabilities can help identify residual risks.