CVE-2025-57820 is a high-severity vulnerability affecting versions of the Svelte utility library 'devalue' prior to 5.3.2. The vulnerability is categorized as CWE-1321, which involves Improperly Controlled Modification of Object Prototype Attributes, commonly known as prototype pollution. Specifically, the issue arises because the devalue.parse function accepts a string input that can represent an object containing a __proto__ property. The parsing logic does not properly validate whether the indices used are numeric, allowing an attacker to manipulate the prototype chain of JavaScript objects. This manipulation can lead to prototype pollution, where an attacker can inject or modify properties on Object.prototype, thereby affecting all objects inheriting from it. Such pollution can result in unexpected behavior, including bypassing security controls, altering application logic, or causing denial of service. The vulnerability is exploitable remotely without authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). The scope is high because the vulnerability affects the integrity and confidentiality of applications using the vulnerable devalue versions. The issue was fixed in version 5.3.2 of devalue. No known exploits are currently reported in the wild, but the high CVSS score of 7.9 reflects the significant risk posed by this vulnerability if exploited.

For European organizations, the impact of this vulnerability can be substantial, especially for those relying on Svelte and its devalue library in their web applications or services. Prototype pollution can lead to arbitrary code execution, data tampering, or denial of service, potentially compromising sensitive data and disrupting business operations. Since devalue is a utility library often used in frontend frameworks, exploitation could affect client-side applications, leading to compromised user sessions or data leakage. Additionally, if used in server-side rendering or Node.js environments, the risk extends to backend systems. The vulnerability's ease of exploitation without authentication increases the threat level. European organizations in sectors such as finance, healthcare, and critical infrastructure, which often use modern JavaScript frameworks, could face regulatory and reputational damage if exploited. Compliance with GDPR and other data protection laws means that breaches resulting from this vulnerability could lead to significant fines and legal consequences.

European organizations should immediately audit their software dependencies to identify usage of the devalue library versions prior to 5.3.2. The primary mitigation is to upgrade all instances of devalue to version 5.3.2 or later, where the vulnerability is patched. For environments where immediate upgrade is not feasible, organizations should implement input validation and sanitization to reject or neutralize any input containing __proto__ properties or suspicious prototype manipulation patterns. Employing Content Security Policy (CSP) headers can help mitigate some exploitation vectors in web applications. Additionally, monitoring application logs for unusual prototype modification attempts and deploying runtime application self-protection (RASP) tools can provide early detection and prevention. Developers should also review their codebase for unsafe usage of devalue.parse and consider alternative libraries if necessary. Regular security testing, including static and dynamic analysis focusing on prototype pollution, is recommended to detect similar issues proactively.