webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies
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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | webpack-dev-server | < 5.2.5 | 5.2.5 |
References
- https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79
- https://nvd.nist.gov/vuln/detail/CVE-2026-9595
- https://github.com/facebook/create-react-app/pull/7444
- https://github.com/webpack/webpack-dev-server/pull/4316
- https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb
- https://cna.openjsf.org/security-advisories.html
- https://github.com/webpack/webpack-dev-server
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Weakness (CWE)
CWE-346, CWE-441- Platform
- npm
- Package
webpack-dev-server- Disclosed
- 17.06.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-mx8g-39q3-5c79 - CC BY 4.0
Vulnerability history: webpack-dev-server
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 01.2019 07.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 1
- Medium 6
Disclosures per year
- 2019: 1
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 2
- 2026: 4
-
webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies this entry
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