CVE-2026-112085: webpack-dev-server vulnerable to cross-origin WebSocket access via proxied upgrades

Vulnerability summary

CVE-2026-112085 is a high (CVSS 8.2) Origin Validation Error vulnerability in webpack-dev-server. EPSS estimates a 0.15% chance of exploitation in the next 30 days, higher than 3.9% of scored vulnerabilities.

Timeline

1. 22-10-2026
   PublishedVulnerability first disclosed.
2. 22-10-2026
   Last modifiedVulnerability information updated.

Description

webpack-dev-server is a development server that provides live reloading for webpack projects. In versions before 5.2.7 and in version 6.0.0, when a proxy entry is configured to forward WebSockets, the server forwards non-HMR WebSocket upgrade requests to the proxy target without validating the Host or Origin headers, so the allowedHosts protection does not apply to those proxied upgrades. A malicious web page visited by a developer can open a cross-origin WebSocket through the dev server and read from and write to the proxied backend, even when the server is bound to loopback. The issue is fixed in webpack-dev-server 5.2.7 and 6.1.0, where proxied WebSocket upgrades pass the same Host and Origin validation as the HMR WebSocket, and users should upgrade to one of those versions or later. As a workaround, omit WebSocket forwarding from proxy entries that do not need it and scope the proxy to specific paths.

• CWE-346Origin Validation ErrorThe product does not properly verify that the source of data or communication is valid.
• CWE-1385Missing Origin Validation in WebSocketsThe product uses a WebSocket, but it does not properly verify that the source of data or communication is valid.