PT-2026-49244 · Webpack Dev Server · Webpack-Dev-Server

Ajhyndman + 2 · Published 2026-06-15 · Updated 2026-06-15 · CVE-2026-9595

Mitre

CVSS v3.1

5.3

Medium

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Impact: When a user-configured proxy on webpack-dev-server has a broad context (e.g. /) and ws: true, it also intercepts the dev server's own HMR WebSocket and forwards it to the proxy target. This leaks the browser's cookies and Origin header to the backend, bypasses the dev server's Host/Origin validation, and corrupts the HMR socket (both HMR and the proxy end up writing to the same socket).

Patches: Fixed in webpack-dev-server@5.2.5.

Workarounds: Scope user-defined proxy context to specific paths instead of /, or omit ws: true from the proxy entry when WebSocket forwarding is not required.

Fix

Origin Validation Error

Weakness Enumeration

CWE-346

CWE-441

Related Identifiers

CVE-2026-9595

Affected Products

Webpack-Dev-Server

References · 6

• https://nvd.nist.gov/vuln/detail/CVE-2026-9595 · Security Note
• https://cna.openjsf.org/security-advisories.html · Note
• https://github.com/facebook/create-react-app/pull/7444 · Note
• https://github.com/webpack/webpack-dev-server/pull/4316 · Note
• https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79 · Note
• https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb · Note