CVE-2026-9595

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.

How to fix CVE-2026-9595

To remediate CVE-2026-9595, upgrade the affected package to a fixed version below.

• —upgrade to 5.2.5 or later

Is CVE-2026-9595 being exploited?

No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-9595.

Affected packages (1)

• from 0, < 5.2.5

CVSS scores

References (7)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-9595
• PATCHgithub.com/webpack/webpack-dev-server
• WEBcna.openjsf.org/security-advisories.html
• WEBgithub.com/facebook/create-react-app/pull/7444
• WEB