CVE-2025-59057 is a cross-site scripting (XSS) vulnerability classified under CWE-79 that affects specific versions of the React Router library, a widely used routing solution for React applications. The vulnerability arises in the meta() and <Meta> APIs when operating in Framework Mode, specifically during server-side rendering (SSR) where script:ld+json tags are generated. These tags are intended to embed structured data in JSON-LD format for SEO and rich snippets. However, if untrusted or unsanitized input is incorporated into these tags, the improper neutralization of input allows an attacker to inject arbitrary JavaScript code. This injected script executes in the context of the victim's browser, potentially leading to theft of sensitive information such as cookies, tokens, or other session data, and could facilitate further attacks like account takeover or privilege escalation. The vulnerability does not affect applications using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>), which handle routing differently and do not generate these vulnerable script tags. The flaw has been patched in @remix-run/react version 2.17.1 and react-router version 7.9.0. The CVSS v3.1 score is 7.6 (high), reflecting network attack vector, low attack complexity, requiring privileges and user interaction, with high confidentiality impact but limited integrity and no availability impact. No public exploits are currently known, but the widespread use of React Router in web applications makes this a significant risk if unpatched.

For European organizations, this vulnerability poses a significant risk especially for those deploying React applications using server-side rendering with the affected versions of React Router in Framework Mode. Exploitation can lead to client-side code execution, enabling attackers to steal sensitive user data such as authentication tokens, personal information, or perform actions on behalf of users. This can result in data breaches, regulatory non-compliance (e.g., GDPR violations), reputational damage, and financial losses. Industries with high reliance on web applications, such as finance, e-commerce, healthcare, and government services, are particularly vulnerable. The attack vector being remote and network-based increases the threat surface, especially for public-facing applications. Although exploitation requires some privileges and user interaction, the impact on confidentiality is high, which is critical for protecting user privacy and trust. The lack of availability impact means service disruption is unlikely, but data integrity and confidentiality risks remain substantial.

European organizations should immediately audit their React applications to identify usage of @remix-run/react versions between 1.15.0 and 2.17.0 or react-router versions between 7.0.0 and 7.8.2, particularly those using Framework Mode with meta() or <Meta> APIs generating script:ld+json tags. The primary mitigation is to upgrade to @remix-run/react version 2.17.1 or later, or react-router version 7.9.0 or later, where the vulnerability is patched. Additionally, developers should ensure that any data used to generate script:ld+json tags is strictly sanitized and validated to prevent injection of untrusted content. Implement Content Security Policy (CSP) headers to restrict script execution sources, reducing the impact of potential XSS. Conduct thorough code reviews focusing on SSR data handling and consider adopting Declarative or Data Mode routing where feasible, as these modes are not affected. Monitoring application logs for unusual script injection attempts and user behavior anomalies can help detect exploitation attempts early. Finally, educate development teams about secure coding practices related to SSR and JSON-LD generation.