CVE-2025-54803 is a high-severity prototype pollution vulnerability affecting versions of the js-toml JavaScript TOML parser prior to 1.0.2. js-toml is a library designed to parse TOML 1.0.0 specification-compliant configuration files into JavaScript objects. The vulnerability arises from improper handling of object prototype attributes during parsing, allowing an attacker to craft malicious TOML input that modifies or adds properties to the global Object.prototype. This type of prototype pollution (CWE-1321) can lead to unexpected behavior in applications using the vulnerable library, potentially enabling remote code execution, denial of service, or data manipulation without requiring authentication or user interaction. The CVSS 4.0 score of 7.9 reflects its high severity, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges or user interaction needed (PR:N/UI:N), but with high scope and impact on confidentiality, integrity, and availability (SC:H/SI:H/SA:H). Although no known exploits are currently reported in the wild, the vulnerability is critical due to the widespread use of JavaScript TOML parsers in web applications, server-side environments, and configuration management tools. The issue is resolved in js-toml version 1.0.2, and upgrading to this or later versions is essential to mitigate risk.

For European organizations, this vulnerability poses significant risks, especially for those relying on js-toml for configuration parsing in web applications, cloud services, or internal tooling. Exploitation could allow attackers to manipulate application logic, escalate privileges, or disrupt service availability, potentially leading to data breaches, service outages, or compromised integrity of critical systems. Given the lack of authentication or user interaction requirements, attacks could be automated and launched remotely, increasing the threat surface. Sectors such as finance, healthcare, government, and critical infrastructure in Europe could face operational disruptions or regulatory compliance issues if exploited. Additionally, the high scope impact means that a successful attack could affect multiple components or services within an organization, amplifying damage.

European organizations should immediately audit their software dependencies to identify usage of js-toml versions below 1.0.2. Upgrading to version 1.0.2 or later is the primary and most effective mitigation. For environments where immediate upgrade is not feasible, implementing input validation and sanitization on TOML files before parsing can reduce risk. Employing runtime application self-protection (RASP) or web application firewalls (WAF) with rules to detect and block suspicious TOML payloads may provide temporary defense. Additionally, organizations should monitor logs for anomalous parsing errors or unexpected prototype modifications. Incorporating dependency scanning tools into CI/CD pipelines to detect vulnerable js-toml versions will prevent future introduction of this risk. Finally, educating developers about prototype pollution risks and secure coding practices when handling untrusted input is recommended.