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CVE-2026-9595— webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies

Quick assessment

Affected
webpack-dev-server webpack-dev-server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

webpack-dev-server webpack-dev-server是webpack-dev-server的开发服务器。 webpack-dev-server存在安全漏洞，该漏洞源于代理配置不当，当用户配置的代理具有广泛上下文（如/）且启用ws:true时，会拦截开发服务器自身的HMR WebSocket并将其转发到代理目标，导致浏览器Cookie和Origin标头泄露给后端，绕过开发服务器的Host/Origin验证，并破坏HMR套接字。以下版本受到影响：5.2.5之前版本。

CVSS 5.3 · Medium EPSS 0.23% · P13

Affected Version Matrix 2

VendorProduct Version RangeStatus
webpack-dev-server webpack-dev-server < 5.2.5 affected
5.2.5 unaffected
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I. Basic Information for CVE-2026-9595

Vulnerability Information
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Vulnerability Title
webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
源验证错误
Source: CVE Program / CVE List V5
Vulnerability Title
webpack-dev-server 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
webpack-dev-server webpack-dev-server是webpack-dev-server的开发服务器。 webpack-dev-server存在安全漏洞，该漏洞源于代理配置不当，当用户配置的代理具有广泛上下文（如/）且启用ws:true时，会拦截开发服务器自身的HMR WebSocket并将其转发到代理目标，导致浏览器Cookie和Origin标头泄露给后端，绕过开发服务器的Host/Origin验证，并破坏HMR套接字。以下版本受到影响：5.2.5之前版本。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
webpack-dev-server webpack-dev-server 0 ~ 5.2.5 -

II. Public POCs for CVE-2026-9595

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III. Intelligence Information for CVE-2026-9595

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Patches & Fixes for CVE-2026-9595 (2)

Vendor Advisories for CVE-2026-9595 (1)

IV. Related Vulnerabilities

Same product: webpack-dev-server
Same vendor: webpack-dev-server
Same weakness: CWE-346

V. Comments for CVE-2026-9595

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