CVE-2026-6402: Webpack.js Webpack-Dev-Server

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

webpack-dev-server versions up to and including 5.2.3 are vulnerable to cross-origin source code exposure when serving over a non-potentially trustworthy origin such as plain HTTP. The previous fix relied on the Sec-Fetch-Mode and Sec-Fetch-Site request headers, which browsers omit for non-trustworthy origins, allowing a malicious site to load the bundled source as a script and read it across origins. Impact: an attacker controlling a website visited by a developer running webpack-dev-server can recover the application source code when the dev server runs over HTTP at a guessable host and port. Chromium based browsers from Chrome 142 onward are not affected due to local network access restrictions. Upgrade to webpack-dev-server 5.2.4 or later, which sets Cross-Origin-Resource-Policy: same-origin on responses.

Affected products

• Webpack.js Webpack-Dev-Server: before 5.2.4 (fixed in 5.2.4)

Published 2026-05-12. Last modified 2026-06-17.