CVE-2025-55183 is a medium-severity vulnerability identified in Meta's React Server Components framework, specifically in versions 19.0.0, 19.1.0, and 19.2.0, including packages react-server-dom-parcel, react-server-dom-turbopack, and react-server-dom-webpack. The vulnerability arises from unsafe deserialization practices (CWE-502) and results in the exposure of sensitive system information (CWE-497). An attacker can craft a malicious HTTP request targeting a Server Function that exposes a stringified argument, either explicitly or implicitly. This crafted request causes the server to return the source code of any Server Function, effectively leaking internal application logic and potentially sensitive implementation details. The vulnerability does not require authentication or user interaction, and the attack vector is network-based, making it remotely exploitable. The exposure of source code can facilitate further attacks, such as identifying additional vulnerabilities, understanding business logic, or crafting more effective exploits. The CVSS v3.1 base score of 5.3 reflects the medium impact on confidentiality, with no impact on integrity or availability. No patches are currently linked, and no known exploits have been reported in the wild as of the publication date. The vulnerability is particularly relevant for applications that rely on React Server Components in the specified versions and configurations where Server Functions expose stringified arguments.

For European organizations, the primary impact of CVE-2025-55183 is the potential leakage of sensitive source code and internal logic of web applications using vulnerable React Server Components versions. This exposure can aid attackers in reconnaissance, enabling them to identify further vulnerabilities or weaknesses in the application stack. While the vulnerability does not directly compromise data integrity or availability, the confidentiality breach can lead to intellectual property theft, exposure of proprietary algorithms, or reveal security controls and business logic. Organizations in sectors with high reliance on web applications—such as finance, e-commerce, healthcare, and government—may face increased risks if their applications use the affected versions. The medium severity indicates that while the risk is not critical, it is significant enough to warrant prompt attention, especially in environments where source code confidentiality is paramount. Additionally, the lack of authentication requirements lowers the barrier for exploitation, increasing the threat surface. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate the potential for future attacks.

European organizations should first inventory their use of React Server Components, specifically checking for versions 19.0.0, 19.1.0, and 19.2.0, and the related packages react-server-dom-parcel, react-server-dom-turbopack, and react-server-dom-webpack. Where vulnerable versions are identified, organizations should prioritize upgrading to patched versions once available from Meta. In the interim, developers should audit Server Functions to ensure they do not expose stringified arguments unnecessarily, minimizing the attack surface. Implement strict input validation and sanitization on all Server Functions to prevent malicious payloads. Employ network-level protections such as Web Application Firewalls (WAFs) to detect and block suspicious HTTP requests targeting Server Functions. Restrict access to Server Functions through authentication and authorization controls where feasible, even though the vulnerability does not require authentication, to reduce exposure. Monitor application logs for unusual request patterns indicative of exploitation attempts. Finally, conduct regular security code reviews and penetration testing focused on deserialization and information disclosure vulnerabilities in React Server Components.