Unintended Proxy or Intermediary ('Confused Deputy') Affecting webpack-dev-server package, versions <5.2.5
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applications- Snyk IDSNYK-JS-WEBPACKDEVSERVER-17353649
- published17 Jun 2026
- disclosed15 Jun 2026
- creditUnknown
Introduced: 15 Jun 2026
CVE-2026-9595 (opens in a new tab)How to fix?
Upgrade webpack-dev-server to version 5.2.5 or higher.
Overview
webpack-dev-server is an Uses webpack with a development server that provides live reloading. It should be used for development only.
Affected versions of this package are vulnerable to Unintended Proxy or Intermediary ('Confused Deputy') via permissive user proxy configurations that include a broad context and enable WebSocket forwarding. An attacker can cause the interception and forwarding of the dev server's own HMR WebSocket, leading to the leakage of browser cookies and Origin headers to the backend, bypassing Host/Origin validation, and corrupting the HMR socket by having both the proxy and the dev server write to the same socket.
Workaround
This vulnerability can be mitigated by scoping user-defined proxy contexts to specific paths instead of '/', or by omitting 'ws: true' from the proxy entry when WebSocket forwarding is not required.