CVE-2021-25941 is a critical prototype pollution vulnerability found in the 'deep-override' JavaScript library versions 1.0.0 and 1.0.1. Prototype pollution occurs when an attacker is able to manipulate the prototype of a base object, which can lead to unexpected behavior in applications that rely on that object. In this case, the vulnerability allows an unauthenticated attacker to inject or modify properties on the Object prototype, potentially altering the behavior of the application using the 'deep-override' library. This can result in denial of service (DoS) conditions by causing application crashes or infinite loops, and in some scenarios, it may lead to remote code execution (RCE) if the polluted prototype properties are used in sensitive operations such as dynamic code evaluation or command execution. The vulnerability is exploitable remotely without any user interaction or privileges, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). The severity is rated critical with a CVSS score of 9.8, reflecting the high impact on confidentiality, integrity, and availability. The vulnerability is classified under CWE-1321, which relates to improper handling of prototype pollution. Although no public exploits have been reported in the wild, the potential for severe impact makes this a significant threat to applications that incorporate the affected versions of 'deep-override'. Since 'deep-override' is a utility library used in JavaScript environments, particularly in Node.js applications, any software or service relying on these versions is at risk. The lack of official patches or updates at the time of this report further increases the urgency for mitigation.

For European organizations, the impact of this vulnerability can be substantial, especially for those developing or deploying Node.js applications that depend on 'deep-override' versions 1.0.0 or 1.0.1. Exploitation could lead to service outages due to denial of service attacks, disrupting business operations and causing financial losses. More critically, if remote code execution is achieved, attackers could gain unauthorized access to sensitive data, manipulate application logic, or pivot within internal networks, leading to data breaches and compliance violations under regulations such as GDPR. The widespread use of JavaScript and Node.js in web services, cloud applications, and internal tools across European enterprises means that this vulnerability could affect a broad range of sectors including finance, healthcare, government, and technology. The potential for automated exploitation without authentication increases the risk of large-scale attacks. Additionally, the reputational damage and regulatory penalties resulting from successful exploitation could be severe. Organizations relying on third-party software that includes 'deep-override' may also face supply chain risks if those dependencies are not properly audited and updated.

European organizations should immediately audit their software dependencies to identify any usage of 'deep-override' versions 1.0.0 or 1.0.1. If found, they should upgrade to a patched or secure version of the library as soon as it becomes available. In the absence of an official patch, organizations can implement temporary mitigations such as sandboxing affected applications, employing runtime application self-protection (RASP) tools to detect prototype pollution attempts, and applying strict input validation to prevent malicious payloads from reaching the vulnerable code paths. Additionally, code reviews should be conducted to identify and refactor any unsafe usage patterns of 'deep-override' that could be exploited. Monitoring network traffic and application logs for unusual behavior indicative of prototype pollution or exploitation attempts is also recommended. Organizations should engage with their software vendors and open-source communities to track patch releases and advisories. Finally, incorporating software composition analysis (SCA) tools into the development lifecycle can help prevent future inclusion of vulnerable dependencies.