CVSS 3.1
4.3 mediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:LCVE-2026-9595
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.
Severity
- EPSS
- 0.2% chance of exploitation in the next 30 days; higher than 5% of CVEs (scores of 2026-10-31)
- CWEs
- CWE-346, CWE-441
- Published
- Modified
- Record from
- the NVD, synced
Affected
- webpack.js:webpack-dev-server
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-mx8g-39q3-5c79 | npm | webpack-dev-server | <5.2.5 | 5.2.5 |
References
- https://cna.openjsf.org/security-advisories.html
- https://github.com/facebook/create-react-app/pull/7444
- https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb
- https://github.com/webpack/webpack-dev-server/pull/4316
- https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79