CVE-2025-57353 is a prototype pollution vulnerability found in the Runtime components of the messageformat package for Node.js, affecting versions prior to 3.0.1. The vulnerability arises due to insufficient validation of nested message keys when processing message data. An attacker can exploit this flaw by crafting malicious input that manipulates the prototype chain of JavaScript objects, specifically by injecting arbitrary properties into Object.prototype. This manipulation affects all objects inheriting from Object.prototype, potentially causing denial of service (DoS) conditions or unexpected application behavior. Since JavaScript objects share the prototype chain, altering the base prototype can lead to widespread impact across the application lifecycle. Notably, this vulnerability does not require any privileges or user interaction to exploit and can be triggered remotely over the network. Although the latest available version at the time of reporting still does not address this issue, no known exploits are currently observed in the wild. The CVSS v3.1 base score is 5.3, indicating a medium severity level, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and no user interaction (UI:N). The impact is limited to confidentiality (C:L) with no direct impact on integrity or availability. The vulnerability corresponds to CWE-1321, which relates to improper validation of prototype pollution in JavaScript environments. Given the widespread use of Node.js in web applications and services, especially those handling internationalization or message formatting, this vulnerability poses a risk of application instability or data leakage through prototype manipulation.

For European organizations, the impact of CVE-2025-57353 can be significant, particularly for those relying on Node.js applications that utilize the messageformat package for localization or message processing. Prototype pollution can lead to unpredictable application behavior, including potential denial of service scenarios or subtle data leakage through altered object properties. This can undermine the confidentiality of sensitive data processed by the application. Since the vulnerability does not require authentication or user interaction, attackers can remotely exploit vulnerable services exposed to the internet, increasing the attack surface. European enterprises in sectors such as finance, healthcare, e-commerce, and public services that depend on Node.js backend services may face operational disruptions or data confidentiality risks. Moreover, the exploitation could be leveraged as a stepping stone for further attacks, such as injecting malicious code or bypassing security controls, if combined with other vulnerabilities. The lack of a patch in the latest version increases the urgency for organizations to implement alternative mitigations. Compliance with GDPR and other data protection regulations in Europe also raises the stakes, as exploitation leading to data breaches could result in regulatory penalties and reputational damage.

Given the absence of an official patch, European organizations should adopt a multi-layered mitigation approach. First, audit and inventory all Node.js applications to identify usage of the messageformat package, especially versions prior to 3.0.1. Where possible, upgrade to the latest available version and monitor vendor announcements for patches addressing this vulnerability. If upgrading is not feasible, implement input validation and sanitization controls to reject or neutralize nested message keys that could manipulate the prototype chain. Employ runtime application self-protection (RASP) or Web Application Firewalls (WAFs) configured to detect and block payloads attempting prototype pollution patterns. Additionally, apply strict Content Security Policies (CSP) and isolate critical application components to limit the impact of prototype pollution. Conduct thorough code reviews focusing on object handling and prototype usage to identify and remediate unsafe coding practices. Finally, monitor application logs and network traffic for anomalous behavior indicative of exploitation attempts, and prepare incident response plans tailored to prototype pollution attacks.