CVE-2026-94485 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 misconfiguration within the development server environment, specifically affecting the next dev command execution context. This issue stems from an insufficient access control mechanism applied to the Model Context Protocol endpoint exposed by the local development server. While production deployments are correctly configured to exclude this sensitive interface, the development mode inadvertently leaves it accessible without robust cross-origin request restrictions. This architectural oversight allows any web page visited by a developer while running the local Next.js application to interact with the internal API endpoints that manage project metadata and diagnostic information.
From a technical perspective, the flaw is classified as an insecure direct object reference combined with broken access control mechanisms in a client-side context. The Model Context Protocol endpoint serves critical operational data including the absolute disk location of the project files, snippets of source code extracted from error reports, a complete inventory of defined routes, and detailed development logs containing runtime information. Because these endpoints lack reliable cross-origin resource sharing restrictions or origin validation checks during local execution, they are susceptible to Cross-Site Request Forgery style attacks where malicious scripts can issue authenticated requests on behalf of the developer's browser session. This effectively bypasses standard same-origin policy protections that would normally isolate web applications from one another in a production environment.
The operational impact of this vulnerability is severe for developers working locally, as it facilitates unauthorized disclosure of sensitive intellectual property and infrastructure details. An attacker hosting a malicious website can exploit this weakness to exfiltrate the project's source code structure, potentially revealing proprietary algorithms or internal architecture patterns contained within error reports. Furthermore, access to disk locations aids in mapping the local file system for further exploitation attempts, while route inventory provides a blueprint of application functionality that could be leveraged during subsequent attack phases. Development logs may contain sensitive runtime data such as environment variable values, database connection strings, or user session tokens if they are inadvertently logged by error handling routines.
This vulnerability aligns with CWE-209, which describes the generation of an error message that reveals sensitive information, and CWE-862, missing authorization checks in critical functions. In terms of threat modeling, it corresponds to ATT&CK technique T1537, where attackers communicate through a legitimate external remote service or protocol to exfiltrate data without triggering traditional security alerts due to the use of trusted local services. The attack vector is primarily web-based and requires user interaction, specifically visiting a malicious site while the development server is active in another tab or window.
Mitigation strategies focus on immediate version updates and operational discipline during software development. Organizations should upgrade Next.js dependencies to version 16.3.8 or later where this access control flaw has been remediated by implementing stricter origin validation for internal endpoints. Developers must also adhere to the principle of least privilege by ensuring that local development servers are not exposed to untrusted networks and by avoiding the logging of sensitive data in error reports during active debugging sessions. Additionally, using browser isolation techniques or dedicated virtual machines for web application development can reduce the attack surface presented by cross-origin interactions between malicious sites and local development tools.