CVE-2026-94486 in Next.js
Summary
by MITRE • 10/02/2026
Next.js is a React framework for building full-stack web applications. From 16.0.0 until 16.3.8, the next dev development server exposes a Model Context Protocol endpoint without reliably restricting cross-site requests. A malicious website visited by a developer can reach the endpoint and read the project's disk location, source code snippets from error reports, route inventory, and development logs. Production deployments do not serve this endpoint. This issue is fixed in version 16.3.8.
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Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified in Next.js versions ranging from 16.0.0 to 16.3.8 represents a significant security oversight within the development server environment, specifically concerning the exposure of the Model Context Protocol endpoint without adequate cross-origin resource sharing controls. As a widely adopted React framework for building full-stack web applications, Next.js provides developers with robust tools for rapid application development and deployment. However, during the active development phase, the next dev command launches an interactive development server that includes various diagnostic and debugging endpoints to facilitate efficient workflow management. One such endpoint is designed to support the Model Context Protocol, a standard intended to allow large language models or other AI agents to interact with local tools and data sources securely. In the affected versions, this endpoint was accessible via HTTP requests from any origin without implementing strict restrictions on cross-site request forgery mechanisms or same-origin policy enforcement. This architectural flaw allows any web page visited by a developer while their Next.js development server is running to initiate requests against this internal API, effectively bypassing standard browser security boundaries that are typically designed to isolate content from different origins.
The operational impact of this vulnerability is severe due to the sensitive nature of the data accessible through the exposed endpoint. Because the Model Context Protocol endpoint lacks proper origin validation, a malicious website can exploit this weakness to read critical project metadata and source code artifacts directly from the developer's local machine or development environment. Specifically, an attacker can retrieve the absolute disk location of the project directory, which may reveal sensitive file paths and organizational structures that are not intended for external access. Furthermore, the endpoint exposes snippets of source code embedded within error reports generated during the development process. These snippets often contain logic related to business rules, authentication mechanisms, or database queries, providing an attacker with valuable insights into the application's architecture and potential weak points. Additionally, the vulnerability allows unauthorized reading of the route inventory, which maps out all available API endpoints and page routes in the application, thereby aiding reconnaissance efforts for further exploitation attempts. Development logs are also accessible, potentially leaking environment variables, configuration details, or other runtime information that could compromise the integrity of the development infrastructure.
It is crucial to distinguish this vulnerability from risks associated with production deployments, as the affected endpoint is exclusively served by the next dev server and is not present in optimized production builds. This distinction limits the attack surface primarily to developers who have their local development servers running while browsing potentially malicious websites or being subjected to drive-by download attacks on compromised sites. Despite this limitation, the risk remains high because developers often run these servers with elevated privileges or access to sensitive internal networks and data stores that are not exposed in production environments. The lack of reliable cross-site request restrictions means that even a simple HTML page hosted by an attacker can trigger automated scripts to exfiltrate this information without any user interaction beyond visiting the site, making it a classic example of Cross-Site Request Forgery combined with unauthorized data access via API endpoints.
To mitigate this vulnerability and align with industry best practices for secure development environments, organizations should immediately upgrade Next.js to version 16.3.8 or later, where the issue has been resolved by implementing proper origin checks on the Model Context Protocol endpoint. Until upgrading is feasible, developers can adopt several defensive measures such as disabling unnecessary endpoints in their local configurations or using browser extensions that enforce strict same-origin policies for development servers. It is also advisable to run development servers behind a reverse proxy that filters incoming requests based on expected origins and implements rate limiting to prevent automated scraping attempts. From a vulnerability classification perspective, this issue maps closely to CWE-942, which describes the exposure of sensitive information through improper access control mechanisms, and aligns with MITRE ATT&CK technique T1530, involving data from cloud or storage systems via unauthorized API calls. By treating development environments with the same level of security rigor as production systems, organizations can prevent accidental leakage of intellectual property and reduce the attack surface available to adversaries seeking to compromise developer workstations.