CVE-2024-51999 is a vulnerability classified under CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes) affecting the Express.js framework for Node.js. Specifically, in versions prior to 5.2.0 and 4.22.0, when the extended query parser is enabled ('query parser': 'extended'), the request.query object inherits all properties from the Object prototype. This inheritance allows query string parameters to overwrite these prototype properties if the parameter keys match property names. Such overwriting can lead to unexpected or malicious manipulation of the request.query object, potentially causing logic errors or security bypasses in applications relying on this data. The vulnerability is exploitable remotely without authentication or user interaction, as it involves crafting HTTP query strings. However, the impact is limited to integrity issues within the application context, as it does not directly expose sensitive data or cause denial of service. The vulnerability was fixed in Express.js versions 5.2.0 and 4.22.0 by preventing prototype pollution via query parameters. No public exploits or active exploitation campaigns have been reported to date. The CVSS 4.0 base score is 2.7, reflecting low severity due to limited impact and ease of exploitation without privileges. Organizations using affected Express.js versions should prioritize upgrading and reviewing query parser configurations to mitigate this risk.

For European organizations, the primary impact of CVE-2024-51999 lies in the potential for attackers to manipulate application logic by overwriting prototype properties in the request.query object. This could lead to subtle security issues such as bypassing input validation, triggering unexpected code paths, or corrupting application state. While the vulnerability does not directly compromise confidentiality or availability, integrity issues can cascade into more severe security flaws depending on the application’s design. Organizations running web applications built on vulnerable Express.js versions, especially those exposing APIs or web services to the internet, face increased risk of targeted attacks exploiting this flaw. The impact is more pronounced in complex applications that rely heavily on query parameters for critical logic or authorization decisions. Given the widespread use of Node.js and Express.js in European tech sectors, particularly in countries with strong software development industries, the vulnerability could affect a significant number of web services. However, the absence of known exploits and the low CVSS score indicate a limited immediate threat. Nonetheless, failure to patch could allow attackers to leverage this vulnerability as part of multi-stage attacks or to facilitate other exploits.

To mitigate CVE-2024-51999, European organizations should take the following specific actions: 1) Upgrade Express.js to version 5.2.0 or later, or 4.22.0 or later for the 4.x branch, as these versions contain the fix preventing prototype pollution via query parameters. 2) Review and disable the use of the extended query parser if it is not strictly necessary, switching to the default or safer query parsing options to reduce attack surface. 3) Implement strict input validation and sanitization on all query parameters to prevent malicious payloads from affecting application logic. 4) Conduct code audits focusing on how request.query data is used, ensuring that no critical logic depends on mutable prototype properties. 5) Employ runtime protections such as object freezing or deep cloning of request.query objects to prevent prototype chain modifications. 6) Monitor web application logs for unusual query strings that attempt to overwrite prototype properties, which may indicate exploitation attempts. 7) Integrate dependency scanning and vulnerability management tools to detect and alert on usage of vulnerable Express.js versions. These targeted measures go beyond generic patching advice and help reduce the risk of exploitation in production environments.