CVE-2021-25916 is a critical prototype pollution vulnerability found in the 'patchmerge' library versions 1.0.0 and 1.0.1. Prototype pollution is a type of security flaw that occurs when an attacker is able to manipulate the prototype of a base object in JavaScript, which can lead to unexpected behavior in applications using the vulnerable library. In this case, the vulnerability allows an unauthenticated remote attacker to inject or modify properties on the Object prototype, potentially altering the behavior of the application that relies on patchmerge for merging JavaScript objects. This can cause denial of service (DoS) conditions by corrupting application logic or data structures. More critically, it may lead to remote code execution (RCE) if the polluted prototype properties are used in a way that allows execution of arbitrary code. The vulnerability has a CVSS 3.1 base score of 9.8, indicating it is critical with network attack vector, no privileges required, no user interaction needed, and impacts confidentiality, integrity, and availability. Although no known exploits are reported in the wild, the severity and ease of exploitation make it a significant threat. The vulnerability is categorized under CWE-1321, which relates to improper handling of prototype pollution in JavaScript. Since patchmerge is a JavaScript library used to merge objects, applications or services that depend on it for object merging operations are at risk if they use the affected versions. The lack of available patches at the time of reporting means users must take immediate mitigation steps to prevent exploitation.

For European organizations, the impact of this vulnerability can be substantial, especially for those relying on JavaScript-based applications or services that incorporate the patchmerge library. Exploitation can lead to denial of service, disrupting business operations and causing downtime. More severe consequences include remote code execution, which could allow attackers to take control of affected systems, steal sensitive data, or move laterally within networks. This poses a high risk to confidentiality, integrity, and availability of critical systems. Sectors such as finance, healthcare, government, and critical infrastructure in Europe are particularly vulnerable due to their reliance on secure and stable IT environments. Additionally, the vulnerability can be exploited remotely without authentication or user interaction, increasing the risk of widespread attacks. The potential for RCE could facilitate ransomware deployment or espionage campaigns targeting European entities. Given the critical severity and the broad impact on JavaScript applications, European organizations must prioritize identifying and remediating this vulnerability to maintain compliance with data protection regulations like GDPR and to protect their digital assets.

European organizations should immediately audit their software supply chain and codebases to identify any usage of patchmerge versions 1.0.0 or 1.0.1. If found, they should upgrade to a patched version as soon as it becomes available or consider replacing patchmerge with alternative, secure libraries that do not have prototype pollution vulnerabilities. In the absence of an official patch, organizations can implement input validation and sanitization to prevent untrusted data from influencing object merges. Employing runtime application self-protection (RASP) or web application firewalls (WAF) with rules to detect and block prototype pollution attack patterns can provide additional defense. Developers should review and harden code that merges objects, ensuring that prototype properties are not inadvertently modified. Monitoring application logs and network traffic for unusual activity related to object manipulation can help detect exploitation attempts early. Finally, organizations should maintain an up-to-date inventory of third-party dependencies and integrate automated vulnerability scanning into their CI/CD pipelines to prevent vulnerable versions from being deployed.