Vulnerability · Published Jun 15, 2026 · Assigned by openjs
CVE-2026-9595webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies
Medium 5.3
In plain English
A medium-severity security flaw in webpack-dev-server from webpack-dev-server. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 6% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu:22.04:LTS | node-webpack | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:24.04:LTS | node-webpack | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:25.10 | node-webpack | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:26.04:LTS | node-webpack | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:26.10 | node-webpack | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:22.04:LTS | vue.js | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:24.04:LTS | vue.js | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:25.10 | vue.js | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:26.04:LTS | vue.js | no fix listed | UBUNTU-CVE-2026-9595 |
| Ubuntu:26.10 | vue.js | no fix listed | UBUNTU-CVE-2026-9595 |
| npm | webpack-dev-server | 5.2.5 | GHSA-mx8g-39q3-5c79 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| webpack-dev-server | webpack-dev-server | 0 – before 5.2.5 |
Weakness: CWE-346, CWE-441 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79
- https://cna.openjsf.org/security-advisories.html
- https://github.com/webpack/webpack-dev-server/pull/4316
- https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb
- https://github.com/facebook/create-react-app/pull/7444