CVE-2025-57323 is a Prototype Pollution vulnerability found in the mpregular package, specifically in the mp.addEventHandler function of versions 0.2.0 and earlier. mpregular is a small program development framework based on RegularJS, which is used to facilitate frontend or JavaScript-based application development. Prototype Pollution vulnerabilities occur when an attacker is able to inject or modify properties on JavaScript's Object.prototype, which is the base object from which most objects inherit. By manipulating this prototype, attackers can influence the behavior of all objects in the environment, potentially causing unexpected behavior or security issues. In this case, the vulnerability allows an attacker to supply a crafted payload to the mp.addEventHandler function, which results in injection of properties onto Object.prototype. The minimum consequence of this vulnerability is a denial of service (DoS) condition, where the application or system using mpregular may crash or become unresponsive due to corrupted object states or infinite loops triggered by the polluted prototype. The CVSS v3.1 base score is 7.5, indicating a high severity level. The vector string (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) shows that the attack can be performed remotely over the network without any privileges or user interaction, and it impacts availability only, not confidentiality or integrity. No known exploits in the wild have been reported yet, and no patches are currently linked, which suggests that affected users should be vigilant and monitor for updates. The vulnerability is categorized under CWE-1321, which relates to improper handling of prototype pollution in JavaScript environments.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on mpregular in their web applications or internal tools. Since the vulnerability allows remote attackers to cause denial of service without authentication or user interaction, it can be exploited to disrupt services, leading to downtime and potential loss of business continuity. This is particularly critical for sectors that require high availability such as finance, healthcare, and public services. Although the vulnerability does not directly compromise data confidentiality or integrity, the resulting DoS can indirectly affect operational integrity and trust. Additionally, if attackers chain this vulnerability with others, it could potentially lead to more severe attacks. The lack of patches means organizations must rely on temporary mitigations until official fixes are released. The risk is heightened for organizations with public-facing applications using mpregular, as these are exposed to internet-based attackers.

1. Immediate mitigation should include auditing all applications and services to identify usage of the mpregular package, especially versions 0.2.0 and earlier. 2. Where possible, isolate or restrict access to services using mpregular to trusted networks to reduce exposure to remote attackers. 3. Implement Web Application Firewalls (WAFs) with rules to detect and block suspicious payloads that attempt prototype pollution patterns targeting mp.addEventHandler. 4. Monitor application logs for unusual errors or crashes that could indicate exploitation attempts. 5. Until an official patch is released, consider applying code-level mitigations such as sanitizing inputs to mp.addEventHandler or overriding the function to reject suspicious payloads. 6. Plan for rapid deployment of patches once available and maintain an incident response plan to address potential DoS attacks. 7. Educate developers about prototype pollution risks and secure coding practices to prevent similar vulnerabilities in custom code.