CVE-2025-55183 is a vulnerability in Meta's React Server Components, specifically affecting versions 19.0.0, 19.0.1, 19.1.0, 19.1.1, 19.1.2, 19.2.0, and 19.2.1, including packages react-server-dom-parcel, react-server-dom-turbopack, and react-server-dom-webpack. The flaw stems from unsafe deserialization of untrusted data (CWE-502) that leads to exposure of sensitive system information (CWE-497). An attacker can craft a specially formed HTTP request targeting a Server Function that exposes stringified arguments, causing the server to return the source code of any Server Function. This leakage of source code can reveal internal logic, secrets, or implementation details that should remain confidential. The vulnerability requires no authentication or user interaction, making it remotely exploitable over the network. The CVSS 3.1 base score is 5.3 (medium severity), reflecting the confidentiality impact without affecting integrity or availability. No patches are currently linked, and no known exploits have been reported in the wild. The root cause is improper handling of serialized data in Server Functions, which can be mitigated by restricting exposure of stringified arguments and improving input validation and serialization safety. This vulnerability poses a risk primarily to web applications built with the affected React Server Components versions, especially those exposing Server Functions to external requests.

For European organizations, the primary impact is the potential exposure of proprietary server-side source code and sensitive implementation details. This can facilitate further attacks such as targeted exploitation, intellectual property theft, or bypassing security controls. Organizations relying on React Server Components for critical web applications may face increased risk of reconnaissance by threat actors. While the vulnerability does not directly compromise data integrity or availability, the confidentiality breach can undermine trust and compliance with data protection regulations like GDPR if sensitive information is indirectly exposed. The ease of remote exploitation without authentication increases the attack surface, especially for public-facing applications. This could lead to reputational damage and increased costs for incident response and remediation. The lack of known exploits in the wild suggests limited current exploitation but also highlights the need for proactive mitigation before attackers develop weaponized exploits.

1. Audit all Server Functions in affected React Server Components versions to identify any that expose stringified arguments or deserialize untrusted data. 2. Implement strict input validation and sanitization to prevent unsafe deserialization. 3. Limit the exposure of Server Functions to trusted internal networks or authenticated users where possible. 4. Monitor HTTP request patterns for unusual or suspicious payloads targeting Server Functions. 5. Stay updated with Meta's security advisories and apply patches or updates as soon as they become available. 6. Consider upgrading to later versions of React Server Components that address this vulnerability once released. 7. Employ Web Application Firewalls (WAFs) with custom rules to detect and block malformed requests targeting Server Functions. 8. Conduct regular code reviews focusing on serialization and deserialization logic to prevent similar issues. 9. Educate development teams about secure coding practices related to serialization and server-side data handling.