CVE-2026-6402
webpack-dev-server vulnerable to cross-origin source code exposure on non-HTTPS origins
Description
### Impact When webpack-dev-server is running on a non-HTTPS origin (the default), cross-origin requests from malicious websites can load the dev server's JavaScript bundles via `<script>` tags. The fix introduced in v5.2.1 (CVE-2025-30359) relied on `Sec-Fetch-Mode` and `Sec-Fetch-Site` request headers to block these requests, but browsers only send these headers for [potentially trustworthy origins](https://w3c.github.io/webappsec-secure-contexts/#is-origin-trustworthy). Over plain HTTP, the headers are absent and the check is bypassed. An attacker who knows the dev server's host, port, and output path can exfiltrate all module source code by intercepting the webpack runtime's module registration. This does not affect Chrome 142+ (and other Chromium-based browsers) due to [local network access restrictions](https://developer.chrome.com/release-notes/142#local_network_access_restrictions). ### Patches Patched in webpack-dev-server >= 5.2.4 by setting `Cross-Origin-Resource-Policy: same-origin` on responses. ### Workarounds Run the dev server with HTTPS enabled (`--https` or `server.type: 'https'` in config). ### Resources - [GHSA-4v9v-hfq4-rm2v](https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-4v9v-hfq4-rm2v) (CVE-2025-30359) - original vulnerability - [GHSA-9jgg-88mc-972h](https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-9jgg-88mc-972h) (CVE-2025-30360) - prior bypass
How to fix CVE-2026-6402
To remediate CVE-2026-6402, upgrade the affected package to a fixed version below.
- —upgrade to 5.2.4 or later
Is CVE-2026-6402 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 5.2.4