CVE-2026-23736 identifies a prototype pollution vulnerability in the seroval library, a tool designed to facilitate JavaScript value stringification beyond the capabilities of JSON.stringify. Specifically, versions 1.4.0 and earlier improperly validate input during JSON deserialization, allowing an attacker to inject malicious object keys that alter the prototype chain of JavaScript objects. This CWE-1321 vulnerability enables an attacker to manipulate the behavior of applications by corrupting object prototypes, potentially leading to arbitrary code execution, data tampering, or denial of service. The vulnerability is exploitable remotely without any authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). The impact spans confidentiality, integrity, and availability, though the confidentiality and integrity impacts are partial, reflecting potential but not guaranteed data exposure or modification. The issue is limited to the JSON deserialization functionality of seroval and is resolved in version 1.4.1. While no known exploits have been reported in the wild, the vulnerability's characteristics suggest it could be leveraged in supply chain attacks or to compromise web applications relying on seroval for complex data serialization tasks.

For European organizations, this vulnerability poses a significant risk especially to those developing or deploying JavaScript applications that incorporate seroval for advanced serialization tasks. Exploitation could allow attackers to manipulate application logic, corrupt data, or cause service disruptions, impacting business continuity and data security. Organizations in sectors such as finance, healthcare, and critical infrastructure, which rely heavily on web applications and JavaScript frameworks, may face increased exposure. The vulnerability could also be leveraged in supply chain attacks targeting software development pipelines. Given the remote, unauthenticated exploitability, attackers could scan for vulnerable instances and compromise systems at scale. The partial impact on confidentiality and integrity could lead to data breaches or unauthorized modifications, while availability impacts might cause denial of service conditions. This could result in regulatory compliance issues under GDPR and other European data protection laws, leading to financial and reputational damage.

European organizations should immediately audit their software dependencies to identify usage of seroval versions below 1.4.1. Upgrading to seroval 1.4.1 or later is the primary and most effective mitigation. For environments where immediate upgrade is not feasible, implementing strict input validation and sanitization on JSON data before deserialization can reduce risk. Employ runtime application self-protection (RASP) or web application firewalls (WAFs) configured to detect and block prototype pollution attack patterns. Incorporate security testing in CI/CD pipelines to detect vulnerable library versions and prototype pollution attempts. Monitor logs for anomalous object prototype modifications and unusual application behavior. Educate developers about the risks of prototype pollution and secure coding practices related to object deserialization. Finally, maintain an incident response plan tailored to JavaScript application compromises to quickly contain and remediate any exploitation attempts.