CVE-2018-14732 in webpack-dev-server
Summary
by MITRE
An issue was discovered in lib/Server.js in webpack-dev-server before 3.1.6. Attackers are able to steal developer's code because the origin of requests is not checked by the WebSocket server, which is used for HMR (Hot Module Replacement). Anyone can receive the HMR message sent by the WebSocket server via a ws://127.0.0.1:8080/ connection from any origin.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2018-14732 represents a critical security flaw in webpack-dev-server versions prior to 3.1.6, specifically within the lib/Server.js component. This issue stems from insufficient origin validation within the WebSocket server implementation that powers Hot Module Replacement functionality. The flaw allows unauthorized actors to establish WebSocket connections to the development server's HMR endpoint at ws://127.0.0.1:8080 without proper authentication or origin verification, creating a significant attack surface for malicious parties who wish to intercept sensitive development data.
The technical nature of this vulnerability aligns with CWE-284, which addresses inadequate access control mechanisms, and specifically manifests as a lack of proper origin validation in WebSocket communication. The WebSocket server fails to implement origin checking as defined in RFC 6455, the WebSocket protocol specification, allowing any remote attacker to connect to the HMR endpoint and receive real-time module replacement messages. This occurs because the server operates under the assumption that all connections from localhost are legitimate, without verifying the actual origin of incoming WebSocket requests.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables attackers to potentially intercept and manipulate the development workflow of web applications. When developers connect to the webpack-dev-server, their code modules are continuously transmitted via WebSocket connections for hot reloading purposes. An attacker who successfully establishes a WebSocket connection can receive these module updates, potentially gaining access to sensitive source code, development artifacts, and implementation details that would otherwise remain private within the development environment. This exposure represents a significant risk for organizations that conduct development work on public or shared networks where such connections might be intercepted.
The attack vector for this vulnerability is particularly concerning as it requires minimal technical expertise to exploit, since the target server is designed to operate on localhost and does not enforce strict origin validation. This flaw can be leveraged by attackers to perform reconnaissance on development environments, collect sensitive code patterns, or even potentially inject malicious code into the development workflow. The vulnerability directly relates to ATT&CK technique T1059.006 for execution via web shell, and T1566 for social engineering through development environment compromise. Organizations should immediately update to webpack-dev-server version 3.1.6 or later, which implements proper origin validation for WebSocket connections, or alternatively deploy network-level restrictions to prevent unauthorized access to development server endpoints.